Prepare a little speech first

Standing there in front of your room, you give it a quick thought how you could approach the delicate subject. 'It's time to stop being fuck buddies'? Naw, a little too direct. 'Hey you know what, I think it's a bit early for me to get a bun in the oven'? Nah, that's a bit too... dramatic.

You take another breath and open the door, and Dennis looks back at you. Your moment to shine. "Hey! It's been great and all, but let's take a break from this for a bit. I think you already learned plenty. If you feel bad in the future we can... we can see what we can do about it, alright?"

"Oh... uhm... yeah I guess?" he replied a little confused while you continue staring at him. He eventually gets the hint, grabs his clothes and gets dressed before giving you a quick kiss. "I'll see ya later then," he added while still trying to figure out what just happened. But, he didn't seem to have the interest, or confidence, to pry into that topic. Quick and easy, just like ripping off a band-aid.

Communication is key, who knows how this could have ended if you hadn't opened your mouth.