The excitement of a new relationship will do that.
The excitement of an illicit relationship will do that.
do you want to be your colleague's rebound FWB ? because it does seem you are headed that way
are you prepared to look for a new job?
prepared to look for a new home on your own while you look for/start a new job?
New illicit romances are exciting. For a while.
In any case, I think you do need to end the relationship you're in. Your partner deserves to be with someone who loves him and wants to be only with him.
What you do about your colleague afterward is a matter to deal with once you're living on your own.