Waswas divorce

Asalamu alaikum i have a question that keeps me very busy.

My husband and i where talking about a woman who had contact with another man while she was engaged. Then my husband said: if you would did that to me (having contact with another man while we where engaged) it would be immediatly over between us. Unfortunately i did had contact with another man while we were engaged and my husband dont know that. Does this count as a divorce? Can a husband make a conditional divorce on something the happend in the past and is that divorce valid?

I’m very confused because we need to conceal our sins right? So i dont know if this is valid or not. I hope you can help me. May Allah reward you