I need help to be a better person for my partner.

Hello, first time posting on this subreddit. Me and my partner has a long talk the other night about how i am to them and that i need to change if our relationship will last. She outlined that I've been incredibly manipulative and emotionally abusive to her to get what i want. I haven't been listening to her before this when shes told me but it hit a breaking point and it needs to change. Whenever something doesn't go my way i threaten to break up with her or something else completely unhealthy. I have emotional breakdowns if something doesn't go how i want it to. I for some reason i don't understand, maybe stupidity maybe mental illness im unaware of, didn't recognize i have been doing these things. I have severe anxiety and heavy relationship trauma that likely influences my actions. That is to say none of this excuses my behavior. Im just completely unsure of how to start changing/ stop doing these things. Shes the love of my life and i need to change if i want her to be with me any longer. She broke off our engagement until she sees some improvement in me. I want to stop being a bad person/ partner to her and save our relationship. Any advice or direction would be appreciated.