bf can’t make me cum

so I’m pretty sure this is a common problem but idk for sure. basically, when my bf and I have sex I just can’t finish. he’s so sweet and he feels really bad about it so he will literally spend a couple hours going down on me, fingering me, touching my clit, etc. but still nothing. I get really close but it won’t happen. the weird thing is that I have no problem doing it on my own. it usually takes like 15 minutes max. it just makes me feel bad because he tries so hard and I would of course love to cum when we have sex lol. any ideas on how to get there and or why it’s not working? thanks in advance!