going down

my boyfriend doesn't like going down on me and I don't know why & he claims he feels like he won't do it right but I've told him a million times that he's can't do anything wrong (as long as he doesn't bite me!😂) anyway he went down on me a few times now and everytime he does he does it for like 2 mins and then he's soft :/ & he doesn't last long enough to make me cum through intercourse, it makes me feel terrible and I don't know what to do? we've spoken about it and he's just said that he's "trying to warm up to it" lol what