How can I be happy?

I’ve been in an abusive relationship. Never gave up, always been back to this guy who treated me horribly, lied and cheated consistently, even though we both suffered because of his mistakes, he kept lying until I had enough and physically weren’t able to handle it anymore.

I want to know how to let go and be happy because I’m in a lot of pain, even though I ended it recently Im having difficulties sleeping etc.