Last weeks of Highshcool, Psycho Ex Girlfriend, Need other male and Female viewpoints

It may be a little long, but hear me out here buddies.
So the cutoff date to turn in work is May 28, which is not too far away. I was extremely behind on school work from suspensions/expulsions but by working my ass off I will be done in the next two days =]. This has been very hard to catch up, but I'm taking a t-break until I am finished as a reward and for motivation as well.

The real problem is this. I had a long term relationship with my first girlfriend, it lasted from the 8th grade to about the beginning of 10th grade. I was working two jobs, playing football and just a good kid. My girl however, was very immature, jealous, and just a horrible girlfriend. She gets this from her mother, who is very immature and I really have no reason as to why I put up with her shit but I did. When I finally left her, it was because she was causing too many problems in my life, and I thought leaving her would be better but it made things a lot harder. She was dating a good friend of mine the next day, and was just all out trying to get me jealous which worked. I got into some bad shit which did not turn around until this year when I realized I need to do something better with myself.

My last relationships have all ended because of her. She always knows when I have a girl, and does her best to put shit into their head which they believe. Her entire family is very childish, which is why I think she knows all she does. They seem to all make fun of me for one reason or another, and although I don't care about it, it gets old real quick. It just pisses me off at how immature and stupid they can be and still feel good inside.

The thing about me is, I am romantic. When I am in a relationship I do all I can to keep my lady happy and let her know I'm hers. The reason for this is, I get my greatness from my females in the sense that they are my motivation. They drive me to be a better man. But this is what I need help with. There is a girl I fancy, who works at a restaurant, and I am slowing flirting with her so I can eventually ask her out. What I don't want though is my ex coming and ruining this. This lady is a good girl ( I can tell) and I know she does not need my exes and her families shit and neither do I. So ladies and gentleman, what can I do to keep this woman, when my ex is a bitch who needs to mind her own, but has no family to teach her to do so?

If you read all that thankyou, and thankyou for the responses as well.

 

Yea that is long.
Short version.

I had a long term relationship with a girl. I left her cuz she was childish. She has broken up my last few relationships and I don’t want that to happen with my next gf. High school is nearly done, and I’m wondering when is she gonna grow up, so any advice would be appreciated.