Moving on from Ex-husband

I’ve been divorced for over 3 years now and my ex-husband has had a girl friend for the last 2 years. She’s been living with him for over a year. When she first moved in I asked around about her because my son spends half the time with his dad. Pretty much everyone I talked to said she was trouble, or just someone they didn’t want to get to know. All of us are involved in rodeo and roping. This is a small circle where everyone knows everybody. So needless to say I run into them a lot. I am still single and I think I’m jealous that I don’t have a relationship. There are times that I think, I wish I had him back. How do I move on? Do I have to figure out how to be nice to the girlfriend?