A frustrating break up

So I've been with my fiance for 4 years. And this past year has been kind of the worst. We had broken up and gotten together several times and although we were having problems we always agreed to be together and work through it. We celebrated our 4 year anniversary on December 1st and I was even able to fund a trip to Disney only to find out a few days later that he was in a 6 month relationship with someone else. And even after confronting him about it, we agreed to keep fighting for us and building this relationship. But then he told me he was in a mental health facility and was in there all week but when it was time to see him again he blocks my calls and messages. Not knowing at the time he was lying, I went to his mother's house trying to make sure he was okay. But that's when I found out his mother thought our relationship ended months ago and he was dating this other girl and he was never in the facility at all. And he told her that the trip to Disney was his plan and he went alone so he didn't waste it, although it was a lie. I'm honestly in shock and don't know what to think or feel. My mental health is shot.

What could have I done differently? And what do I do moving forward?

I still have a lot of his things in my family house in another state but he's not answering me. How long do I let this go on before I have to do something with his things?

I'm so lost and heartbroken and wish I knew what to do from here.