Why did he ditch me for another girl?

My guy best friend of 2 years recently got a girlfriend. He told me so many times that he didn’t want a relationship and that he isn’t ready for one. He was in prison for 16 months and I stayed the entire time he was locked up. He would call me everyday, we would write eachother, and I spent a lot of money on him.. he got out back in June and things just have not been the same. He was hooking up with a 35 year old woman and at the time I felt completely tossed to the side and he would say “im single” disregarding my feelings. He has always known how I felt about him. He always knew that I wanted more. When he was locked up, he never told me what we were or how he felt. I would ask him if we will ever be in a relationship and he would say “I don’t know the future, I can’t promise anything give me time”. He even said that when he got out. Suddenly he has a girlfriend and texted me yesterday asking to be friends when I made it clear from so long ago that I will not be in his life if he gets a girlfriend. It is common sense, Im in love with him. Im just very hurt he basically dropped me for someone else after all I did and I stuck by his side
Why did he ditch me for another girl?
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