Relationships: What is wrong with me?

New to this, but can't figure it out on my own. In one year I have come to the end of a marraige (spell check) and lost two "girlfriends". Of course there are many moving parts to relationships, but the short and sweet of it is that I don't seem to care much about my other half until they want to hit the road. My wife left me, said we grew apart. It seemed like the end of the world but after that I found another lady...wasn't serious by any means to me but once she said see ya later...I couldn't stop trying to get her back. Then comes the next girl. Same deal. Didn't pay her a whole lot of attention, but then after she said goodbye I seemed to act like it was the end of the world again. And again, did everything in my power to try and get her back to no avail. I know it may sound like some sort of teenaged boy's problem, but I am in my 30s. I just don't seem to put much into a relationship until it is jeopardized and that's when I spring into action only to find that's it's far too late to fix anything. Has anyone dealt with anything like this? If so, I'd really like to hear what you have to say. And I know that I haven't been very descriptive but throw some questions at me. I would just really like to get some insight as to why I'm such a dumbass. Thank you in advance.