Relationship advice

So I have been with my high school sweetheart for 3 years now. We are engaged now and he is currently in the Marines and has been for a year and some change now, while I have been away at college (just basically finished off my freshmen year.) In the past he has cheated, but I have learned to get over it. It was like the first couple months we started dating so I kind of let it be. He would lie, here and there about partying and made me upset but whatever. While he was in bootcamp for 3 months I supported him, was loyal to him and all, and that went through the whole process leading to his career in the Marine Corps. (MCT, Schooling, etc) While he was at his schooling I was actually pregnant with our son, which we ended up miscarrying at 7 months. Just a couple months ago I found out (SIX MONTHS LATER) there was a girl that sent him nudes, wanted to have sex w him knowing he has a fiancé and a kid on the way. But yet not once did he tell me about this. When I asked he told me he was "tempted" then argued with me saying that his words came out the wrong way. Anyways fast forward, for my spring break I decided to come to North Carolina where he is stationed. During this visit I had found out that he has been talking to his ex. But not only that but it has been an on going thing and then he just blocks her after. And it hasnt been flirting but he talks to her to insult me... And she does the same thing back and he lets her talk about me like that. (He is drunk when he does this) And this is because I go out to parties with strictly my girls on Thursday's when im away at school (not all the time but sometimes) for like 2 hours and I come back and fall asleep with him on the phone. NOT to mention he tells me he is okay with it, and then the day of he gets mad and doesn't want me to go. I also found out he saw his ex in the summer while I was away at a summer program for college where they take your phones, you do classes and get grant money which takes off your tuition (For those that dont know its called EOF) I dont know if its just a Jersey thing. Basically its like college bootcamp just not as harsh. But he drove four hours away to see her for four hours (they went to the mall.) Yet no one told me about this, I found out from her. Now yesterday night, I had also seen him make a porn twitter account, where he goes on there to watch porn and follow pornstars. And I asked him if he watches porn and he always says no, but that he watches the videos we make. When I found out about this account he said it was an old twitter account from years ago but he made it this february of 2020. I just want the lies to stop, im hurting myself when I know I could do so much better. Someone please help /: