Sex struggles

When it comes to sex I have no problem at getting what I want from my boyfriend, in fact he's always up for making me feel more than satisfied. On the other hand, I find it really difficult to pleasure him for example when he asks me to suck him I will refuse as my sex drive has increasingly decreased. This is hard for him as we've been going out for 5 years & my sex drive has been 100%. We've argued and fallen out as he says he feels ugly, that I don't love him as much as I used to and I just feel like there's something wrong with me:( any suggestions ...