Hey people...could you help me with this one?

right been split up with ex girlfriend of 2 and a half years for about 3months now she has a new boyfriend (she is still with him)...and she ended it with me and her,...pretty sure the reason was for this guy, I haven't spoke to her for a good month...benn on holiday etc getting over it well...recently I've joined a gym...lost 1 and a half stone...got into shape with personal trainer...on a healthy food plan..new clothes...now I have just about finished in college, and I came out to the mive car park and guess who was parked behind my car...the ex...not just parked but sat in there on her own, she knows what time I come out everyday...so I ignored the fact...went to unlock car then she blew her horn a couple of times, I still ignored it then she put her window down and was like "oi how are you?" I said good thanks got to go got personal trainer at 6 then off out see you later...my sister then gets a text when I'm home saying "hi,hope your ok :) can I have your brothers number please? what is that about..then sister didn't reply and she had another text with ex's new number...what is she doing? why all this now? I don't think her boyfriend would be happy if he found out? any help or advice grateful. what shall i do if i see her hanging around again? just had private email from facebook with a friends request and say "hey you, can we talk, i have lost one of my closets best mates! (me) it sucks!"...but i checked her relationship status and she is still in nrelationship...