Perhaps the most twisted relationship ever

Where to begin. I have been dating a guy for 2 years, I met him when I was 25 and he 28. It started as a casual hookup and progressed. He has three young children so we do not live together full time, I see him 3-4 times per week. He has an apartment in another city where they live. Anyway, things were great for a year, then I discovered that he was messing around with a girl he worked with for around 3 months. Even discovered that he told me he could not see me over christmas break because he had to be with his kids, but he came to the city to take her to dinner and stay at a hotel with her. I stupidly forgave him and decided to move on, I did not know all of the details at first. Anyway, after that things got dark. He became crazily possessive. To the extent that he would freak out and threaten to leave because I sent memes on IG to my two friends, that he knows. I couldnèt enjoy a family vacation to FLorida without cnstant texts and calls. Now recently, I got a security alert that he went in and logged into my google account and downloaded my search history. He found porn that I had watched 8 months ago and got physical with me that night. Anyway it is obvious that I should leave but for some reason I always find myself, even this time trying to be the one to make it work. Just looking for some sense talked into me, I do not want to burden those aaround me with this anymore. Oh....also I have put around 30k into this guy personally and with a business we started.