Why would he cheat ?

So I’m 16 and my ex is 20, I gave him everything though we only dated for two months I was a really good gf to him his never been with a girl who doesn’t cheat and lie until me... I was understanding of his work schedule, understanding when you want to hang out with friends and have alone time, I bought him food, cleaned his room, wasn’t jealous, gave him massages when he got home, gave him head all the time especially in the morning when I woke up before him, wasn’t to clingy, spent as much time with as possible but he cheated on me why? And it’s not because I’m immature because I’m not I have a job and I’m going places in life and every time there was an issue I tried to talk it out with him also I’m smart, hardworking and beautiful so what did I do wrong ?