Am I denying him or should he just get over it?

Me and my boyfriend have been living together for four years. Since the beginning of the relationship I've told him I don't want to give blow jobs and it hasn't really been talked about until about a year or so ago when he started asking me for it. I eventually gave in once and now hes constantly nagging me for it. I've told him I don't like them. I'm open to so other things though, as sex and hand jobs and I always offer to do something like that instead when he's asking. I do give in with blow jobs sometimes to shut him up. He says he loves going down on me etc because he loves pleasuring me. I want to pleasure him, but I can't help it, I just don't feel comfortable with giving blow jobs. I've told him it's obviously okay if he doesn't want to go down on me or so.

He says blow jobs are his favourite thing and that he's sad that I'm denying him the best pleasure, and whine about how he'll never get "best thing" (because he says he wants to be with me forever and get married, so if I don't give him blowjobs obviously no one will so he will never get them).

This almost sparks arguments between us. I think he should just accept that I don't want to do it and get over it and stop pressuring me to do stuff I don't want to do, while he thinks that I should give in for his sake and try to enjoy it because it gives him pleasure. So basically we're thinking that the other one is selfish. I don't know how to solve this? We've talked about it so many times, but we just end up acknowledging that we have two totally different mindsets. I can't understand why he keeps pushing me and he can't understand why I don't want to give him what pleasures him the most. Help me out! Our sex life and relationship is great otherwise and he agrees on this. It's just this thing.