Is he a cheater?

Hi i have been with my ex for as little as 5 months and he was the first one to ask me out. Before we got together his ex of almost 2 yrs broke up with him and 2 months later he convinced me he was over her and ready to make me his queen. We were in a long distant relationship as he lived three hours away but visited me once in january and we had a great time. After some time i noticed he stopped putting effort and he was always busy with work until in the end of may we broke up as apparently he did not get over the breakup with his ex. We were in no contact and sometimes he would text me updating me about his life. He did promise me he would come back and that he loved me so much and that he’s only taking time off to better himself for me. As this situation made me upset i decided to end everything with him and sent him a final email but he begged me not to give up on him and that he loved me so much and he was doing all this for me. One day i checked his instagram and found out that he put a picture of him and another girl as his pfp. When i confronted him he swore that it was his cousin but when i asked him to unblock me on instagram and accept my request he started acting weird and saying “i can’t find u in my blocking list” so i said accept my request from my spam account and he said he “didnt receive my request”. I stopped talking to him as he was acting way too weird and he said one day he will be back for me and blocked me again. I don’t understand his childish behaviour and why he lies to get away with things like that. Any tips?