Hookup during a breakup

A while back (almost 5 1/2 years ago) my then boyfriend (now husband) and I split up very briefly. For like 2 weeks.

Today I found out that he had sex with his ex fiancé. He claims he was drunk and thought it was me but remembers everything (and I mean everything) that happened between them.

We weren’t together but it took him over 5 years to tell me!

We’ve had a lot of issues, especially involving his ex and I’m having a hard time processing that this actually happened.