Why is this please HELP?

I just started working voluntary in a charity shop.I do model work also.i Got on well with the guy that owns it he is chatty,and asked me whoI was seeing.then his gilrfriend walked in.since that she has been there everyday,recommending a hairdresser to me, her guy (my boss) has suddenly turned nasty to me,and she is always walking around showing her authority in front of me.the other ladies think it is strange also.what does thi mean??