Only if her friend does too.

"You can't cum- at least not yet," you say, "If you cum without permission, I'm going to spank BOTH OF YOU until you can't sit down for a week. Got it?"
"Yes, Master."
"Now let me check something out..."

You rest the flogger on Terri's toned back and rub her pussy. She reflexively moves at your touch, but her bondage puts a stop to that.

She's wet.

"You are pretty wet, ****. Is it from the spanking or from my other **** smothering you with her ass?"

Donna steps forward, freeing the MILF's mouth.

"Both," she mutters, "I love both of them."
"Terri! What are you- MMPHHH"

You shove your cock back into Sabrina's mouth, cutting her off.

"So here is how this is going to work. You can only cum when you friend here does," you explain, grabbing Sabrina's hair sharply.

You gesture for Donna to resume smothering Terri and she does. She spreads her ass cheeks as best she can, making sure that the woman rubs her pussy.

In turn, you start to whip the woman's ass, giving it to her harder than ever. She seems to love it.

After a few minutes, you feel her pussy quiver against your touch and you know that she must be close. You make Donna move again.

"Are you going to cum, slut?"
"Yes, Master. May I please cum from your whip?"
"That depends. Are you going to cum with her, ****?"

You pull your cock out of Sabrina's mouth and she quickly answers.

"Yes, please let me cum. I've been holding it for five minutes!"
"You both may cum on the count of 3. 1....2.....2 and a half....3."

Both MILFs cry out in orgasm, but that is quickly smothered by your a combination dick and Donna's ass!

When they finish, you both move away.

"Now that we're all ready, someone is going to get fucked by me. Will it be you," you ask, grabbing Sabrina by the hair, "Or you?"

You give Terri's ass a firm smack as you finish, making her quiver a little more.