FWB situation 😓🙄 sorry this is kind of long

So I met this guy last year (end of Oct.2015) through one of my friends & I really liked him. We started texting & stuff & the more I learned about him & got to know him, I just became so infatuated with him. I've never been in any type of relationship & I was really hopeful for something with this person. We were just texting/hanging out or whatever for like 2 months & finally asked him where are we going with this? When I asked him he proceeded to tell me that he didn't want to be in relationship & I respected his reasons as to why he made this decision, but I was also mad because he would say things to me that led me to believe otherwise 🙄, so we just agreed to be FWB. We finally have sex (Jan.2016) & it was AMAZINGGGGGG 😭. I literally had to fight off any feelings I had for him because I didn't want to get attached being that he didn't want to be in a relationship. We continued to have sex (up until Sept.2016) & it just got better each time. So we've been having amazing sex for like 9 months. A month ago, I went to his twitter page & I saw that he has a girl as his header picture. I was suspicious of it, but was just like whatever because we're nothing more than FWB. The following night, he tweets a picture of them together & that's when I knew something was up. I then text him & he tells me that the girl is his girlfriend. I was very confused because he told me that he didn't want to be in a relationship because he was graduating from college (Dec.2016) & then gets in a relationship 2 months prior to graduating. I felt disrespected because I found out via twitter instead of him. He said he didn't know how to tell me, but I would've been okay & all he had to do was respectively discussed this with me. 

Was I not good enough for him? What is she doing that I'm not? I could've been the best girlfriend ever to him, but he didn't want to find that out. I have my head on straight, in college, with realistic life goals & aspirations, & so does he. I feel like the way I feel is my fault because I could've decided to cut him off & found someone that wanted to be in a relationship, but I chose to remain in this situation with him. He wanted to still be cool & I wished him the best in life. Guys are super confusing 😒

Btw: I  did like him at first, within that 2 months we were hanging out & stuff, but because he showed me that's not what he wanted, I let that go with no problem & I don't shame him for what happened, I just would've rather him talk to me about it.