Closure

I want closure on an ex relationship and I feel bad as I'm in a long term relationship. It isn't that I want to be with my ex it's just I want to close a chapter on this. My ex won't talk to me anyway as we had an argument last time we spoke. I've tried forgetting but I always come back to needing closure. No one might be able to advise but I'd love to not feel so alone with this as I have no one to talk to.