Trouble with myself

So I was in a nasty relationship months ago and it lasted for about 2 years. I can honestly say that it did some damage to me emotionally, and romantically. My problem now is that I am talking with a guy who is really sweet and we are both interested, it's almost official, but I have some problems with myself. Anytime we are talking and another girl comes around or I know he's texting another girl (like the ex did, only he did it romantically and cheated on me multiple times), I feel as if I want him to go behind my back. I know that I shouldn't feel this way, but I do and I hate it honestly. Any siggestions ladies, I would really appreciate it!