Is it normal to fantasize about other guys while having a boyfriend ?

I (29M) have a boyfriend (31M). We're together for 4 years now. I can imagine live with him for the rest of my life but our sex life isn't satisfying me (that's the only problem I have. On his side, he is satisfied).

I fantasize about other guys. My BF's dick is small, and I would love to suck on a massive cock ! But I don't want to break up or cheat. Are those sexual fantasies with other guys normal ? How can I satisfy my desires ? Are sextoxs an option ? I can't imagine new sexual pratices with my partner would be enough. I'm actually not really interested in having sex with him anymore.

Is my situation normal ? Did any of you managed to resolve a similar situation without cheating ?