Their dynamic is interesting to me, I'm not really sure if I've figured it out yet. I don't think they're necessarily romantic, I don't think Simon is emotionally available enough for a romantic relationship. They're definitely closer than friends so they probably have a qpr thing going on once Simon is able to give back to the dynamic a little more and accept Yancy as a friend. Yancy sees a ton of himself on Simon, like he was probably exactly like him when he was first incarcerated and he knows how shitty it feels to be on edge like that all the goddamn time and while he still projects an aura of "untouchable toughness" to this day, he knows when to drop it and be genuine with people. He's really really good at reading people and knowing who to trust, and to Simon's absolute confusion, Yancy seems to trust him immediately. Simons never had that before, for for awhile he just thinks Yancy is dumb as bricks, too trusting of The Butcher and tries to scare him away. It probably takes a fistfight between them and Simon actively betraying Yancy's trust to realize that Yancy isn't as walk over able as he thought. As soon as he's without that comfort he feels terrible, but he best at figuring things out under stress, so he takes that space from Yancy to process their friendship.