Boyfriend and Bestie going behind my back?

ALL WOMEN! I need help!! 😱😱
So I'm in UNI.
My ex and I have been seeing each other lately. We usually hang out in the study hub which is for all students.
He says he would be with me if he could but unfortunately at this stage it's not an option.
We are very close and have shared all of our "firsts" together.
Lately my friends has been talking about my ex and I quite a bit. She always talks about how attractive he is and how she should just date him because at least his parents would like her. 
(Side note- his parents don't like me because I'm not white).
She never used to come to the study hub but now she does quite often.
She comes over and chats very often.
The other day she tussled his hair (as a joke.. I think) and laughed randomly.
Yesterday my ex and I were playing a card game and I suggested we move to another part of the study hub (I suggested a places that was near my friend)
he didn't really want to and I could see it in his body language etc and he sort of said he didn't want to. 
Then he looked over and obviously saw she was there.
Then he said "will Amy play?"
And I said yes most likely and he was like "okay then let's go!"
And that caught my attention...
Then he went to touch my leg but looked over at my friend first.
She couldn't really see us but we could see her from where we sat.
We are also having a joint birthday and she insisted that my ex come.
Should I be worried or am I overreacting?