When Matt orgasms, like fully lets go, his enhanced senses make it a totally overwhelming experience. Full-on tantric orgasms with total loss of composure and control, can't help the noises he makes, just totally wrecked and overtaken. The problem is that it also makes him really vulnerable for an extended period of time - he can't keep track of what's going on around him, wouldn't be able to respond even if he could tell he was in danger. His life experiences, and Stick's training, make that unacceptable. So he doesn't let himself really get off on the occasions he does have sex. He works to keep himself in control, maybe fakes the occasional orgasm, etc.

Then he has sex with Foggy, and everything changes. Because FOGGY is someone he trusts, completely. Foggy is safe. Matt can be vulnerable with Foggy. So he lets himself go, and Foggy LOVES IT.

+Bonus points for Matt being insecure about how raw and uninhibited he is when he lets himself orgasm, and Foggy reassuring him after how FUCKING HOT THAT WAS JFC MATT.

+My soul for glorious description of Matt having a long, long, intense orgasm.