How Can I Avoid This Awkward Situation?

I'm 16 years old and I'm only out to a few friends and my brothers but I met a boy (let's call him Liam) and we came out to each other (he's bi, I'm gay). We've been texting and hanging out a ton over the past few months and I really like him. We've gone to third base and I love being with him but I find it difficult to cum. I've only been able to cum one of the four or five times we've been together. I'm worried that it's because I have a really weird fetish that seems to turn me on more than boys do. When I jerk off I try not to watch my fetish porn too much but recently it has been difficult for me to orgasm with regular gay porn. Does anyone have any tips that may help me be able to orgasm with Liam? It's embarrassing and frustrating for me when I can't and I don't want to tell him that it's because of the fetish because I don't want him to know about it. I know there may not be much I can do but I just wanted to ask in case anyone has been in a similar situation.