Having a hard time letting go. Why is Ex still acting like this?

My ex of 2 years broke up with me almost a month ago. Our relationship had a lot of drama. I really wanted it to work and invested a lot of time into it, but in the end, we were at 2 different places in our lives. I wanted to be serious, she wanted to do "her own thing". It was a hard breakup for me, but I'm determined to get over it. I'm trying to keep busy, meet new friends. I was at a restaurant/bar the other night out with some new friends. I run into her. Last place I expected to see her. I make small talk with her and her friends, even gave them a little hug. After about a minute, I say I'm going to go and return to my friends, she said I didn't have to go, but I did anyways. I continued having a good time. That night, I get 7 straight texts from her, asking why I acted like that? Then a few more just asking "why"? I didn't want to respond at first, but I did. I said "you mean, surprised to see you, because I was" She's like "you acted so weird". So I replied "I thought I was polite. Oh well" She replied "why are you being ? It's so unlike you?" so i replied "I gave each of you a hug" no reply.
What was that all about? I was so polite

The other day I clicked on her Facebook page and it looks like she met someone already too! This was upsetting...