Giving blowjobs

So I really want to make my boyfriend happy and he never pressures me to do anything I wouldn’t like. We have talked about how I get grossed out by cum because I start gagging and last time he wore a condom so I wouldn’t get any in my mouth but the same thing happened I just started gagging and he got off and the condom filled with cum and I couldn’t stop gagging. Why am I like that? I really want to like it because I know he really likes it and he’s fine with me not doing it because he knows how I am. Is there anything I can do to fix me not liking it?