How do I get back ex back?

well me and my ex broke up, she dumped me said she can't trust me anymore, and she wants to be single. I begged, and I cried, and still nothing came of it. We still live together, she says she just doesn't know right now about getting together and that she's happy being single. I'm not sure how long do I have to wait for her to come back or if she ever will come back again. In the mean time, someone else came along, I guess she makes me happy, and she keeps me occupied from being depressed and emotionally unstable about trying to get my ex back, and then when my ex finally told me she still just want to be single, I told my ex fine, I guess I will have to let you go, but at least you can be happy for me that I have someone that I can move on to, and she's a good girl and I won't be bothering you anymore. Then my ex flipped out and was like if you are messing with her, you can't mess with me, like she started to act like there was a possible chance we might have gotten back, but since I started seeing someone, she was like it's final. We are still in each other's lives some way some how, but I feel the distant, I feel like she really can't trust me or want me back after all this. But she says she still loves me, and I love her, it's just that she has major trust issues with me and now she doesn't want to give me another chance. I want to know when it's over, why do girls care whether or not the person they dump is with someone else? Why do girls get mad about that, and also this new girl is really good to me, but I know if my ex asked me to come back, I would probably end everything with her, but since my ex isn't asking me to come back, and dunno if she will ever, should I be waiting or just move on and if she comes back, she comes back, if not, then just move on. What is best? keep contacting her and making myself available, or ignore her and be with this new girl, what's more effective. I know this a serious of questions, but just answer 1if you can't answer all. I know sometimes if you leave your ex too long, then you may never get her back, but should I just let her completely go for now, and hopefully that when she's with someone else, she will usually realize I'm still the best for her, what do you girls think??? A girl's perspective is helpful.How do I get back ex back?
Don't you ask this weekly?