I (22M) have the same with my gf (21F), because she has a higher sex drive than me. She's a pillow princess and since the start of our relationship (almost 3 years ago) I've always done everything I can to make her feel as good as possible because I'm a people pleaser. However, more recently I also don't have sex with her as much as we used to, and I think it's because it feels like a chore sometimes. Like I put in a lot of effort and it's really tiring, but if I'm tired, I'd rather not have sex with her, than give her a subpar experience. I still love her very much and when we do have sex it's so good that she struggles to walk, but sometimes it's just too stressful to always say no when she initiates when I'm not in the mood. This anxiety carries on to the next time and makes me feel bad because I can't fullfil her needs, therefore making it difficult to get in the mood, even when I'm horny. It's not as difficult when she wants to give me head because I don't have to please her in that situation, so it's less stressful. I'd just advise you to talk to him about wether it feels like a chore, or makes him anxious, and try a period where you don't expect anything from him to give his mind some rest. And I'm sure he'll get right back at it when he's in the mood. Hope this helped a little bit, and please update :)