Contacting an ex

There is nothing wrong with it, but be careful. He can take it as wanting to get back together, even if you make it clear that you do not want to. Usually, it is difficult to remain friends with an ex, partly because your lives have probably gone in different directions since you were dating, so do not be surprised if you catch up with each other briefly and then lose touch again after a couple of weeks, or a month or so. And that is completely natural, if that happens be glad you caught up with each other and then move on.

Theres nothing wrong with it, as long as the person you are dating is aware of it. I am married and I talk with a few old boyfriends through emails, its fun to catch up. The computer has made the world alot smaller now, and easy to reach out to old friends and boyfriends, go for it, and have fun

Leave him alone.  If he harbored any interest in you, he would have looked you up.  He may be involved in another relationship and you need to respect that.  You didn't get along as a couple before so it's probably safe to say that things (and you both) haven't changed to the point where it would work now.  Move on and don't create problems for you or him.  Sorry to sound so harsh, but you've got to face reality and quit wasting your time.  There's someone else out there for you somewhere.  Don't waste your time pretending that something can work when it won't.

In my opinion, I think that you should leave him alone, if he wanted to contact you, he would have done so already.  Try to find other friends to chat with.  He may have someone special by now.  You just don't know how she may react to this if she knew you were contacting him.