You need to have a very direct conversation about your wants and needs. Counseling (couples or individual) may help as well.

Long-term partner ... or roommate? :-(

Did they mention that you may be fat?

What reaction do you want? It's dreams. You can't control what you dream about and being upset about someone's dreams would be stupid.

sieze the moment

I think the fact that you've gone years with him not interested is your first clue your relationship has big issues. Maybe you should talk to each other. why stay in a relationship where neither of you are happy.

Because he’s actually sleeping with other people.

Years of no sex? How can you and why would you stay with them for that long? Have you guys tried counseling?

Honestly, please go to a doctor low sex drive can actually be a symptom of serious things, adrenal cancer for one.