Am I insane or is this normal?

I've been with my ex fiance for 4 years and have been in love with him since i was 18. When i met him i was a virgin but he wasn't. For the years he was with me he fucked up and cheated or fucked someone else as soon as we "broke up" but never was official. I always took him back and still loved him unconditionally because our bond was incredible. I never had a best friend like him. I never have been with someonr I've been so comfortable with and had a great time with. But when things got rocky he would bounce and treat me as if i didn't matter at all. Anyways we recently broke up officially because he wanted a three way with a coworker of mine and i said no... he added her on fb behind my back and i was furious. I went home on my lunch break to question him and he held me and told me how much he loves me and that he would marry me on Thursday (his day off which would have been today). But i said no and told him this doesn't show me he is capable to be my husband. Not even hours later did he message my coworker and try to hook up with her... i saw all the messages and supposedly she blocked him. Yet i still find myself making excuses for him. His brother is in the hospital and recently got pulled out a boxing match because the coaches felt he wasn't in the right state of mind. I feel like him spiraling down made him go crazy and fuck up our relationship.
I'm hurt and want nothing to do with him but i find myself wanting to spiral back and hold on to him and say its ok. I want to be his friend again and be in love with him again but i know he isn't worth my love anymore. Maybe he never was... i guess i feel he would change and love me and be the man i hope he would be.
Anyways what should i do? Reach out to him or stay away? But the obvious answer is stay away.
I feel so stupid for even asking but i need to ask... i need someone to give me their advice.
Am I insane or is this normal?
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