So what is the temperature on Y moving out? And he can live alone/with roomie? And he gets his wants for quieter domestic arrangements and more alone time with you in his new flat? Has that been discussed? Or how about YOU move out. They sort themselves out on their own (since you cannot control their behavior) but you reach out for your own sanity/wishes? (Because YOU can control your own behavior.)
These feelings scare the crap out of me, because I feel like they may force me to have to choose between Y and E, instead of being with both of them like I want.
It is ok to feel scared. It's part of accepting that when you want to be with 2 other people? For that to work out? Those 2 other people have to want the same thing too. It is not just about what you want because they too have voices in the things that concern them. It also means learning to come to terms with disappointment if things come to a conclusion you do not wish for.
Could ask DH to clarify what "sex" is to him. PIV or PIA? Other things? Or any sexual situation at ALL? Even to the mildest hand holding two 10 year old could be doing?
There's a spectrum there to define. Maybe something here could help in that conversation seeking understanding?
What are your OWN wants, needs, and limits you want E to meet? Have you asked if he's willing to meet them? For how long?
What are your OWN wants, needs and limits that you want Y to meet? Have you asked if he's willing to meet them? For how long?
What are each of them wanting from you and are you willing to meet each of those wants, needs, and limits?
Sort yourselves out and talk.