I hate to say this but if your ex told you that you're too jealous and clingy then he must know what he's saying.
Read here
https://tr.im/t8rxg
Anyone that goes out clubbing just to see what their ex is doing or drive by his place at 7:00 a.m. to see who's there tell me that you need to work on something. I don't think that you are only jealous but also possessive. And if you don't change that then you will never get your ex back. Please don't get me wrong. I'm not trying to mean to you. I only want you to see what you are doing is so wrong. You have to admit that you are jealous and clingy. If you can't admit that then you'll never be able to fix the problem.
I understand that you don't like it if he dances and flirts in front of you. But guys are guys. And many guys don't see anything wrong with this. I know you feel hurt if he does that in front of your face. And it is disrespectful. But there are ways you can talk to your boyfriend if he's flirting while he's with you. You only have to tell him that it hurts you and that it's disrespectful and then ask him to stop doing it when he’s with you.
I don't know if getting back with your ex is going to last because now you have two problems. You were having problems with him because of his flirting and now you will have another problem because of this girl that he's going out with. It is eating you alive that he's involved with this girl and you know he's probably sleeping with her. How are you going to handle that if you get back together? Because of your jealousy and your insecurities are you going to be able to forget that he was ever involved with this girl? You really need to work on this and make sure if you try to get him back that you never again mention about his flirting or this girl. You can mention one more time how his flirting affects you but it has to stop there.
You asked how do you compete with the girl he's involved with. I looked at the picture and I can tell that your ex knows how to go for beautiful girls. So that give me a clear picture about how you look. I have a feeling that you are also very beautiful but for some reason I don't think you see yourself that way. The only thing I can tell you is that your boyfriend did not leave you because he didn't love you. He left you because of your jealousy and because you were clinging to him. If you love his as much as you say you do then fight for him and get him back. And if you do get him back then make sure that you can promise him that you will no longer be jealous, clingy or insecure about your relationship with him. If you can't promise him that then you may as well forget about him because it won't work if you don't change,