I guess...

Spurred on by both Sid, and Alyssa, you grab the chastity cage.

You: "Just for a couple of weeks?"

Sid: "yeeeaaah, bud, just temporary... don't worry, I'll keep the key, around my neck, so it doesn't get lost."

You take the cage, drop your pants in front of Sid and Alyssa, and stuff your dick in that small, constrictive, cage. It is see through, and has a slit in the front to allow for urination. Stuffing your dick into that slightly too small cage, you snap it shut. You immediately regret your decision, this is super uncomfortable.

You: "Actually, this isn't a good idea, please take it off, Sid."

Sid: "mmm...I don't think so, bud...not just yet. You need to finish the training..." He says, rubbing the key on his chest between his fingers.

You: "But this hurts! Alyssa, tell him to take it off, please!"

Alyssa: "uhm...sorry, babe...Sid thinks this is for the best....I'm sure you can do this!"

Sid: "You'll get used to it....as a reward, I'll let you shower with Alyssa. Doesn't that sound good?"

You: "...yes..."

So, finally you get naked with Alyssa in the bathroom, and Sid is nowhere in sight! This gets you really excited, but the more excited you get, the more the damn cage hurts. You hug Alyssa from the back in the shower, massaging her wet, bare, breasts. Your dick hopelessly stuck in it's plastic prison, posing no threat of you and Alyssa having sex. She can't even give you a handjob now....

Alyssa: "I'm so glad you're doing this for us, babe. I feel so connected with you, and comfortable. No need to be shy if your dick is in...there."

Alyssa rubs your cage, giving you a slightly good feeling, but any arousal is quickly punished with more pain.

Alyssa: "Wanna suck my pussy, babe? I bet Sid would be fine with it....I'm kinda horny...."

You're excited to suck Alyssa's pussy without Sid's cum in it, so you agree. Your dick straining against the walls of your cage, you get Alyssa moaning heavily in the shower. After a minute, the door opens, and in pops Sid and his massive cock, already erect. The key to your cage around his neck.

Sid: "Thanks for getting her ready for me, Matt. That's a good cuckold..." Sid says as he pushes you the to side, making you fall on the shower tile. He pins Alyssa to the wall, and lines his cock with her pussy.

Alyssa: "ooohhh, Sid...fuck me...."

Sid: "That's my pussy...." He says as he inserts himself deeply in your girlfriend's pussy. You can do nothing but watch as Sid fucks your girlfriend in the shower in front of you. Your dick is trying it's best to be rock hard, but the cage stops it, causing you to be in constant pain.

Sid: "Hear that, cuck? You'll never get this pussy, only I get to fuck it."

Alyssa: "mmmooohhh, fuck....I'm all youuuurrrss..."

You sit there on your knees, cage around your pathetic dick, while Sid fucks your girlfriend.

You: "...wh...what? You said..."

Sid: "I said I'd train you....ugh...fuck....but I wasn't training you to fuck Alyssa....I was training you to be a sissy cuckold, you stupid... fucking....idiot." his sentences are punctuated by his cock going balls deep in Alyssa's pussy.

You: "I....Alyssa..." You look at Alyssa in desperation.

Alyssa: "I'm....sorry...baby....but...this is... probably.... better for everyone." She's timing her sentences in rhythm with Sid's fucking her.

Sid: "She's right...you'll be happier this way, trust me, Matt. You were a born cuckold....give it a chance...."

You: "No! I don't....what are you talking about!?"

Sid: "I'll show you....I've been cumming inside your girlfriend's unprotected pussy for weeks now. She's ovulating right now....I'm gonna cum inside her again, I'm gonna impregnate your girlfriend...you okay with that, cuck?"

The thought of Alyssa actually becoming pregnant with this homeless man's baby, turns you on beyond belief. Your dick feels like it's going to explode, you grab the cage with both hands, your cheeks go red and you say: "n..noooo...."

Alyssa: "It's alright, babe. Just accept it, we can raise it together....Sid has never impregnated anyone before....and he's an old man, it's now or never....and I can do that for him!"

You feel powerless to stop this, all you can do is place your hand meekly on the back of Sid's thighs, while he keeps fucking your girlfriend.

You: "P...please don't impregnate my girlfriend, Sid...!"

Sid: "Shut the fuck up, cuck. After I cum in her, you can suck my cum out. If she gets pregnant, it's your fault."

Sid speeds up fucking Alyssa now, he and her are loudly moaning through the sounds of their wet flesh slapping together. You sit there, your dick exhibiting feeling that you haven't felt in weeks, watching your girlfriend have unprotected, reproductive sex with this homeless man. You can feel tingles moving throughout your spine, going all the way down to your dick. It feels wonderful...

Sid: "aughh...here it comes, I'm fucking coming inside your girlfriend again, cuck! Watch me impregnate her!"

Sid's butt tenses up and inserts himself deep in Alyssa's pussy while he pumps her fertile womb full of his cum. At the same exact time, your dick starts leaking many weeks worth of cum onto the shower floor. You're orgasming, but you didn't touch your dick, you can't even get an erection, it both hurts and feels good at the same time. You and Sid groan in unison as you cum on the shower floor, and Sid cums inside your girlfriend.

Sid: "uuughhhh yeahhh....fuck that's good pussy...." He looks down at you, your dick still painfully leaking cum on the floor. "See, Matt? You're a born cuckold...."

Alyssa: "I'm so glad you liked it, babe..."

They finish the shower together, you try to clean Alyssa's pussy with your mouth, but she wouldn't let you. Preferring to keep Sid's cum in her.

After cleaning the shower, you go to the kitchen, where Sid and Alyssa are laughing together.

You: "What's so funny?"

"Oh, nothing" they say together, both eyeing your crotch, your cage is bulging out your pants in a weird way.

You: "a....are you really trying to get pregnant...?"

Alyssa: "No, babe, that was just to get you riled up. That was Sid's idea, he felt bad you've been unable to cum, so we had to step it up a notch."

Sid: "Hope there's no hard feelings, we were...putting on an act for you. And it worked wonders, you came like a faucet..."

You: "None of that was true? But...you have been cumming inside Alyssa for the past weeks, surely her safe days are up?"

Sid: "True, but I had my sperm count measured, I'm infertile." He pulls out an official looking piece of paper, stating a sperm count of 0. No risk of pregnancy....

You: "Oh..."

Sid: "So we can have all the fun we want, no need to hold back, right? I can cum inside Alyssa's pussy all I want..."

You: "Right....yeah...."

Alyssa: "oooh, I'm so glad, baby. I really love feeling Sid's cum shoot in me, and now I know you love seeing it too!"

And so it went. You kept sleeping in the guest room, while Sid and Alyssa fucked their brains out every day. Sometimes they would lock their door, forcing you to stay outside. Often they would let you watch and smell them, every once in a while you came through the little slit on your chastity cage, when Sid would come deep inside of Alyssa's unprotected pussy.

On your birthday, Sid actually unlocked your cage. Feeling the open air on your dick was enough for you to get a raging erection, and cum right there on the spot. Alyssa and Sid laughed at you. You're pretty sure your dick has shrunk a bit after staying in the cage for so long....after your dick shrivels up after ejaculating, Sid hands Alyssa the cage, she snaps it back on.

Alyssa: "Look how sensitive you've become, baby. This is clearly doing you so good. I love you" she says as she kisses the top of your cage.

You: "I love you too..."

After a couple of months, you've gotten so into the fantasy of Sid impregnating your girlfriend, that at this point your begging for him to cum inside her. It's becoming the only way you know how to cum...

You: "Cum inside your pussy, Sid..." You say, your face up close to their genitals as they fuck in the missionary position. "Flood her with your cum"

Sid: "ugggh, yeah...that's a good cuck....I'm gonna impregnate your girlfriend, Matt! Ggrrrrnnn...fuck!" And you watch in amazement as Sid's cock and balls spasm wildly, as he cums inside Alyssa for the hundredth time. You start feeling that tingle of electricity again, and leak cum on the floor. You have now become the official sex cleanup crew, responsible for licking up your own cum from the floor, as well as sucking Sid's cum out of Alyssa's pussy, and cleaning Sid's cock and balls with your mouth.

One day, Alyssa and Sid are sitting in the kitchen, hand in hand, looking lovingly into each other's eyes.

You: "What's going on?"

Alyssa: "It's a miracle, babe. I'm pregnant!"

A wave of cold terror washes over you. You've been enjoying the fantasy, knowing that it won't come true. You stand there white faced, Sid and Alyssa smiling.

Sid: "I guess my swimmers are stronger than I thought! Aren't you going to congratulate us?"