Partner goes limp with most sexual encounters – advice needed

I (F18) have been with my partner (M18) for over a year now. We started having sex soon after we started dating (prior to this we’d known each other for around 6 years). The first time my partner was not able to stay hard or finish, which was alright with me because he was really nervous about doing it for the first time.
But I find that every time we did (after he started getting comfortable) he goes limp. Sometimes it’ll be after a while, but for the most part it’s before we have sex (soft during/after foreplay) or during sex. The only way for him to get hard (or if he goes soft in the middle of sex) is for his to jack himself off. I’ve learnt to accept it, but it bothers me a lot because he’s soft during everything, including handjobs and blowjobs. I’ve asked him multiple times if what I’m doing is alright (which he tells me yes) and to teach me how to please him (he shows me) but nothing works and I’m super frustrated because it’s like me vs. his hand and I never win. I can’t give him a handjob because he won’t get hard/stay hard, blowjobs are basically the same. He’s never cummed from either unless he was the one touching himself. We’ve explored many positions, and the only ones he’s been able to cum in are missionary, him on top of me while I lay on my stomach and doggy. I don’t have an issue with any of these positions, but I like having the control (and he’s into the sub/dom dynamic) so riding is amongst my favourites. However, he goes limp pretty quickly when I go on top. He tells me that I’m good at it and all, but I just feel like I’m doing something wrong. I do it in the motion he likes, too.

I feel like the breaking point was today, when he wanted to try out ropes on himself (prior to dating we talked about things we were into, and I have more of a dominant side while he enjoys the idea of being a sub like mentioned above). I, being into the idea of him tied up, would be alright with that, so I set him up. He seemed a bit hard at first (while tying him) and I continued with what I was doing (touching him, kissing him, licking him, etc… stuff that he likes) but when I thought he was ready he just wasn’t. Tried other things in hopes of getting a reaction, nothing. He had to go back to jerking himself while tied to get half hard and just told me to try riding, but like every other time, he went soft after a few strokes. He eventually just gave up and went back to having sex in the positions he usually cums in to finish. I cried later & it might’ve been because there was no aftercare, or maybe my birth control making me sensitive, but also (probably/moslty) because of all of that.

On top of that, he often would critique me and say that I don’t dominate him well enough even though I’ve tried so many different things, he just doesn’t react to anything (no matter how I talk to him or treat him). So that upsets me too.

Back to the encounter today, he found me crying in my bed and lay down next to me to try and comfort me. He asked me what was wrong, and I just asked him if I was doing something wrong because he never really stays hard. He just told me that he gets tired and that it has nothing to do with me.

Something to keep in mind is that he jacks off 1-2x a day, everyday. He uses reddit as his way of watching pornographic content (not super often though). I’ve asked him before to try and cool down with jacking off and the reddit porn, but even if he doesn’t jerk off for a few days prior to us seeing each other, he’ll still go soft.

Outside of sex, everything is fine. I treat him well & he does the same. We view our relationship as a long lasting one, so we’re hoping to be with each other for a long time.

I just want to know what can be done. Are we possibly not sexually compatible? Am I doing something wrong? Should I push him more to stop jacking off (if that’s even what’s causing him to go limp)? What do I do if he just can’t stop consuming porn and touching himself?