What am I feeling?

I had been married to my ex for 9 years when I found out about his affair of 2 years. I left him, got into a depression, went to therapy and healed. A year and half later I met my boyfriend, we’ve been dating for 7 month now and he’s the most amazing and genuine person I’ve ever been with and we are very much in love. Today I found out my ex signed a rental contract with his girlfriend (the one that used to be his mistress), and I’m not sure what I’m feeling? Betrayal? Why am I still so hurt over this? Our divorce is about to be finalized and I’m in a really good place in my life right now. But why does this feel so weird!?!