Why am I feeling this way? ?

I just recently got out of a relationship for three years and it's really effecting me. He was the one that suggested seeing other people because I have "some trust issues", but in all honesty his actions were a bit untrustworthy and suspicious. Now that we are no longer together I found out he did do some things that betrayed the trust in our relationship, but still for some reason I'm still caring about what he does now. He and I have known each other for nearly 10 years and I really don't want to lose the friendship we once had. But now I'm not sure if I want him as my friend or if this is my way of wanting him back. What the hell is wrong with me? Any suggestions as to why I am feeling this way? Why do I even still care?