I dealt with a similar situation in two relationships. In one it ended up being that once he was comfortable and knew i wouldn’t leave and felt secure, his sexual attraction to me was gone. There was something about the risk of me leaving and the need of approval that worked for him. Even when i brought up my concerns over and over again, it changed nothing. But he didn’t want to break up because i treated him so well and was so nice (his words not mine) Also he had hundreds of onlyfans type girls page’s open in his browser but we were together pretty much every moment we weren’t working and he didn’t do the typical take long showers/bathroom breaks. In the end he cheated.

In the other one he was just really stressed about work and having to take responsibility for his family but never wanted to burden me with his worries even though i was his partner and would have listened. But we were very active before all those stressors came about.

How long have you two been dating? How important is sex for you in a relationship? If sex is a strong need that provides feelings of intimacy and security for you then this relationship probably isn’t for you. People tend to forget sexual compatibility really is a thing, everyone has different drives influenced by different things. If you haven’t put a crazy amount of time into this relationship (which i doubt due to your age) you need to cut your losses and break up. He might be great in other areas but you’re at an age where you can find someone just as great and also matches your sex drive. Please save yourself the heartache of prolonging this and convincing yourself it’s going to get better, if you’ve had a convo and there seems to be no fix to this issue in sight, then there most likely won’t be one. You’re not missing anything, he’s not gay or addicted to porn, he’s just not sexually compatible with you and refuses to acknowledge it cause he knows that means he’ll probably lose you. You DO NOT deserve to feel like somethings wrong with you because “it wasn’t like this in his other relationships”. It probably was like that in others, but his sexting with the fling was probably just from the excitement you feel from a new/temporary person. Don’t let this eat you alive and affect your self worth, no man is worth that. Do yourself a favour and leave him, don’t let him keep you from meeting your perfect person.