Why did my ex do this? ill amswer urs!?

my and have been spilt up gor about 1 and a half month which is longer our actually relationship. she ended it because she said wasnt ready for a relationship but i found out she want to see other guys espacalliy this one. She broke up with after only knowing him a guy for one week, and has been seeing him ever since we broke up. i know the guy isnt looking a relationship and is leading her on. I have been friendly to my ex even though she made me feel useless and lile i didnt matter. Yet i still tired to be friends with her. I was talking to her the other day and she turned round and asked *did i muck you about* and i turned to her and said yes you did. She said *i wasnt trying to* but i returned saying i know but you still did and that was the end of it. Her whole expression changed and she look sad so in class i said *listen dont worry about it. what done is done and we are still friends* she replied *im not worrying about it* i then said *promise* but kept going off subject. Can someone tell me what this means? Why is asking me now after a month and a half of our break up and it was her broke up woth me! any who can help it welcome