Boyfriend problems

So I dated this guy back in December to February and we broke up because of some stupid girl that bullied me and decided to ruin my relationship, I'm 15 and he had just turned 17, he took my virginity and has cheated on me numerous amounts of times and I still take him back, he's now 18 and I'm 16 next week and he  started talking to me again about 2 weeks ago, I let him back in my life just to find out he's seeing another girl, no matter how many times he does it though I will always still take him back, someone please help me because I don't want someone to be able to walk all over me like that ❤️❤️❤️❤️❤️