One of Peter’s worries is that those he loves will be taken away. I think after his parents leaving him, Uncle Ben dying, he has some pretty strong abandonment issues and when he looses his girlfriends (or they leave him), it just adds to that sense of being left alone which manifests into him thinking there’s something wrong with him and that’s why people leave.

And then Deadpool shows up.

Deadpool who can’t die. Deadpool who comes back with a vengeance. Deadpool who likes staying with Peter and being with him.

Peter keeps waiting for Wade to leave so he distances himself, he keeps Wade at arms length because like so many people in his life, Wade will see something in him that everybody else has seen and he’ll leave Peter and Peter is just waiting for the day for it to happen.

But Wade doesn’t leave. He stays. And it terrifies Peter because what if he lets Wade get close and then the universe pulls the rug from under them?

So Peter keeps Wade at arms length, and uses humour as a way of protecting his heart, and enjoys whatever time he and Wade have together, holding it close to his heart because its only a matter of time before Wade leaves and Peter will be on his own again.