idk what to do😕

theres this dude ive been talkting to for over a year and throught the whole time we were talking hes had multiple girlfriends, but we still messed around.. around the end of the school year last year we finally started dating. All of a sudden i was at a friends house nd he broke up with me because it didnt feel the same, which i didnt understand because we were basically running around hiding the entire time. so after we broke up i had like two relationships that didnt work well. Me and this boy had the BIGGEST fight over something and were really mean to each other....couple months passed and we’re bestfriends and i start dating his “bestfriend”. that lasted a couple of months then and this boy were still really good friends and hooked up after my ex an i broke forward a few weeks, HE HAS A GIRLFRIEND ! so we decided not to mess around anymore, but that didnt last long...he claims he wants to be with her for a long time but he doesnt want me with other people, he said this exactly “i just feel like youre mine, even though youre not, i dont wanna see you with other people but me” I DONT KNOW WHAT TO DO........please help