My husband (24m) won’t stop going to his ex I (25f) asked for a divorce but refuses to give it to me, any advice?

Hi everyone I decided to share my business on Reddit today because I am wondering how many people have fought for marriage fter betrayal. Me (25F) and he is a (24M) we have been married for a little over 3 years and we share kids together. I want to mention that this is the second time I caught him texting his ex venting to her about our problems. He goes and creates fake snap chat accounts to get a hold of her and this happens every time we get into serious arguments. I confronted him about this and he told me the truth he didn’t deny anything, he claims that he just has the feeling of “friendship” for her but I don’t believe anything he tells me. I told him that I want a divorce and I am no longer interested in being with him and he refuses to give me one. He tells me he wants to fight for our family and he is even willing to go to couples therapy with me. I am confused and I am fed up with his actions I just can’t tolerate any of his behavior any longer. Any advice would be appreciated.