Giving head

I feel so bad because my bf is so comfortable with giving me head but I’ve never really done it for him. I’ve given him maybe two or three sucks but then i freak out and pull away and he’s always super supportive and said he doesn’t want me to do it until I’m comfortable so thats not a problem. I want to give it to him but i always chicken out and idk. I think it’s the pre cum in my mouth that’s what’s getting to my head which is a big part of giving head but if i can’t get past that, how am i supposed to do it