Ah, unrequited love for metamours! The bane of the poly world!
Maybe getting together with him while she is in the same apartment isn't the hottest idea ever in what comes to protecting your heart right now. Can he for example visit you?
Blogs that have the same problematics as yours and that I am familiar with are AnnabelMore's Story of a Secondary (similar dynamics to yours) and TeamD79's Life Alien to Our Own (pretty much exactly your situation in many ways).
Me: bi female in my twenties