how do I explain this feeling?

I just recently broke up for good and successfully day 4 into maintaining no contact, this was an exhausting and toxic relationship for both of us and after going on and off for two years, i have let him go.

I don't even know who broke up with who, it just suddenly ended after a fight and we stopped talking and we are not reaching out, like you know when it's different and over good, it's that kind of feeling, something I am both relieved and saddened by. I don't know if I will hear from them again or come across them again, chances are low. I am happy we both will be eventually at peace but am also scared that if I ever come across him with someone else, i can't handle it and spiral in regret and guilt so that makes me sad, but at the same, my gut is saying I won't even remember all this pain and if that ever happens, seeing him with someone else or seeing him alone doing well without you, you won't feel anything inside just indifference. But the thing is, I don't know, none of it makes sense, what I truly feel about this, peace or grief, it's all a blur.

How do I explain this feeling?