What does this mean guys? Why do guys do this?

My guy best friend (been best friends since preschool) and I started talking and hanging out again after I moved back home with my daughter after being in a 5 year abusive relationship. He had also just gotten out of a bad relationship more recent than mine. We flirt and joked around a lot and then he took the next step and pined me on the bed and kissed me. We then slept together. After we slept together I wondered what would happen between us now and if we where going to be a couple now because we've always flirted with each other ever since I could remember. I asked him "What now?" he told me that he wasn't ready for a new relationship and I told him that I understood that. That he could take his time on what would happen next. He didn't talk to me for 2 months. Then after not talking for months and making my mind go crazy thinking I lost my best friend or even if I had done something wrong. He tells me that he now has a girlfriend. What the hell is he trying to hind something or acting like it didn't happen. I mean he won't even tell me anything about his new girlfriend. He hasn't posted anything on any other his social media about a new girlfriend. I don't understand this like guys come on can't you just tell a girl how you feel or you know tell them something so us girls aren't losing are mind about shit like this and then posting questions like this one site like this one. I'm frustrated and confused because I've had feelings for him since middle school and I've always been on and off confused on how he felt about me. What does this mean?
What does this mean guys? Why do guys do this?
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