ex boyfriends mom

So, I was in a relationship for over a year.  We broke up, on semi good terms, lol.  Well it's been about 3 or 4 months since we've broken things off, but his mom keeps on coming into my work (I work in a local coffee shop) and checking in on Facebook, and she told me she's only doing it to make his girlfriend jealous and so she will see that she was there.  I don't want to be a part of that, so what do I say?  His girlfriend is a little jealous, she came in one day and had no clue I worked there.  So now his mom is doing this.  I have not spoken to him since the day we broke up.  So why is she doing this? I'm dating someone else, so it's not like I'm getting back together with him.  What would you do in my situation?