In love with my ex still

My ex and me still keep in touch and meet up whenever we get a chance as currently he has a new girlfriend. I miss the familiarity of it all even though we dated only a few months and also feel a deep connection to him which makes it easy for me to open up and share my innermost feelings with him. Anyways to cut a long story short, I lost him due to my childish behavior and immaturity but that was a year ago and now I really feel that I have matured somewhat. Sadly its too late now as he has recently begun to see another girl. I really wish I could win him back. I know it sounds selfish but I don't think the girl really loves him as she seems to be treating him like an ATM machine. Please advise. Thank you in advance.

When it comes to emotions and feelings, you only learn by your own mistakes, not those of others.
By that i mean, if he likes this girl then that won't change because someone else has told him she's no good for him, he has to figure that out for himself.
You want him back, then you have to play the game! Bit of flirting, get him interested!
Bare in mind though, going after someone who is in a relationship isn't looked upon to well.