I Fantasize Too Much And I Feel Kinda Guilty

I'm usually a very reserved person, and I'm also been in a relationship for 3 years with someone i really love and would never cheat on. However, my partner hasn't been horny for quite some (because of medications) and I've felt the need to imagine stuff that I would like to do if i wasn't in a relationship with him. I'm pretty sure I love my partner, but i just feel guilty, like i'm cheating on him for just imagining, especially because i like to imagine some things that are beyond his boundaries. I also wouldn't dump him just because of wanting to do these fantasies. It's just that I get so horny and I get off to the idea of doing these things, even if i won't do them.