If you choose one girl over another, what possible reason could you have to continue to engage with the one you passed on?

Anonymous

I've known/worked with him for 3 years he knew her for 2 months he choose her, fine. They met (she doesn't live in the same state) i guess talked for 2 months and she moved here/in with him at month 3 - to which he never told me about her or his new relationship status.

Point is now that i know he will not leave me alone he continues to gaslight me and act like its no big deal and nothing is wrong. I clearly feel differently, he made decisions for himself and now I get to make mine and that is I no longer wish to have him in my life but he will not accept that nor give me my space. We work in the same building but not the same section so there's no reason to interact with him but he continues to find reasons to come over whether it be just to peer in on me or ask work related questions he very well already knows that answers to.

What possible reason could he have to continue to insist on interacting with me?

Updates
1 y
*His relationship as well as this behavior towards me has being going on now for 7 months*
If you choose one girl over another, what possible reason could you have to continue to engage with the one you passed on?
3 Opinion