Why won’t she talk to me any more??

My ex and I broke up in January 2016. She cheated on me and got pregnant. Overtime I forgive her and we remain on good terms. Even hooked up a few times but stopped in 2017. Despite what happened I showed no animosity to her. Days when she was at work and ask for lunch I brought to her. She recently join the military and I basically was her right hand man when she was in there. When she needed things I brought them to base, a ride home from pass I picked her up and dropped her back. When she wanted food to eat I brought it and another things. Lost money on my job to attend her graduation and supported her. We had a decent relationship until last Friday. She saw me out with another woman at the movie theater. She walk up to me and squeeze my arm and ask my how I’m doing and said good then she walked off. I think that’s reason why she won’t talk to me anymore. She ignores my messages and phone calls all the time. When she post on Facebook she was like/reply to everyone else’s comments except mine. The question is why is she doing this when I cared so much for her. She said a while ago she doesn’t want me anymore and we are just friends. It’s the same thing here I’m not romantically interested but just enjoy her company. She said I’m a good friend to her before and she brought me a Valentine’s Day in February to say thanks.
What should I do?