Why does he blame me for everything?

Basically, my ex boyfriend broke up with me because I found out that he had been lying to me about a lot of things, and when I confronted him he was angry that I had found out, and he was angry that I was mad at him for lying to me, he then said I made him lie to me? The main thing he lied about was who he was hanging out with/talking to, he'd tell me he was talking or hanging out with his closest guy friends and then really he would go hangout with random girls, and one of his ex girlfriends who I knew still had feelings for him. We broke up 3 months ago, and we spoke a couple days ago and he still says it's my fault he lied to me because "you wouldn't have been okay with me hanging out with them".. and he's right, I wouldn't have been okay with him hanging out with a bunch of random girls and his ex who's intentions with him are unknown, that still isn't a reason to go behind my back and lie to me, and he knew it'd upset me so why would he even do that in the first place? He did have friends who were girls, but I had met them and knew they were just friends, and he has cheated on all of his past girlfriends except me (I hope). .. but when we last spoke like I said he turned everything on me, he got mad at me for not spending as much money on gifts for him as he did on me, however I was a full time student with a part time job, while he was a full time worker and not in school, if I had the money to get him something nice I did. I just don't understand why he's so angry with me and blaming me for everything
Why does he blame me for everything?
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