I cannot cum during sex

Hey, so I have had a girlfriend for 4 months now. We have sex. But the only possible way I am able to cum is when I jerk off on my side. The same way I always masturbated. Even then, it takes some time. Because of this the sex can take ages. We both like it, but it just doesn't end the way 'it should'.

We have talked about it, she doesn't mind she says and she really means that, she cums. But I do care about it. She says it's all in my head but I explained her multiple times that it's probably this: I have jerked off the same way for the past probably 12 years, my grip became firmer every time, I edged and tried to extend every session as long as possible. I feel like it lost its sensitivity. During sex there is pleasure and it feels great, but if I have to reach like 100% for cumming, I reach probably like 80% maximum and it feels like I have to pee lol?

Is there a way to recover this? And is it probably just to "not jerk off for a while", so also not after sex which means sex without cumming?

Thanks in advance. Curious about you guys with similar stories.

 

Damn, thanks a lot for all the very detailed answers. I will go through them. I don't take anti depressiva (I do take anti histamines for my allergies). We do vary in positions, as well as in who's in 'charge' and stuff like that.

I think it is what @starsandsuns mentioned, delayed ejaculation due to desensitization. It feels like that too. My girl and I had a chat about it and every time we start, I am closest to cumming in the first few minutes when she's not super wet yet - that's the moment when the friction is the highest.

Thanks again!

 

A week has passed, I f'd up. We had sex the past couple of days, where we ended after she orgasmed. I did not jerk off after and I did not cum during sex. However, today the urge got too big and I jerked off.... This might be harder than I thought and maybe some extra effort in reading etc is needed. Not in this thread tho, I think most answers are already given.