I need advice and tips, that's all.

So me and my boyfriend were having sex and he went down on me and all that but when I went to go down on him I just couldn't bring myself to give him a bj. I kinda feel bad cuz every time we have sex I can tell he wants me to do it to him but I freeze up whenever my mouth gets close to it. I've never given a bj before so I'm not even sure if what I'm gonna do is right. Idk. I want to give him what he's asking for but I just can't bring myself to do so. I always feel bad afterwards. To make it worse I can never get myself to orgasm. Not once have I had an orgasm every time we have sex. I feel like I'm doing smth wrong and idk what I'm supposed to do. Can anyone give me advice on what to do? Or at least give me tips? Thank you and have a wonderful day!