Is it normal for my mil to contact hubby's ex girlfriend from the past

I am happily married with my husband of 12 years and with 5 beautiful kids. My husband got his ex girlfriend pregnant 14 years ago while in Uni and they were expelled. They went separate ways despite the ex calling and writing to him and sending pictures of their son in the earlier days. Apparently my husband has moved on and the ex hasn't. She never fails in trying to get in touch with my husband or MIL. Last month, the ex contacted MIL and told MIL about the son coming over on a school trip and meeting his dad for the first time ever without my knowing. MIL was so excited that she started being friends with the ex and liking the sons pics on FB. MIL didn't even think for one minute that i deserved to know about it. She never mentioned it. Like i said, the ex never fails in trying to contact my husband and she made contact with him. Only then my husband told me about it but i had already found out about this on FB..which made me very angry. We talked about it and i've accepted his son because it was his past and the kid is innocent. My problem now is the MIL and ex. MIL has been in frequent contact with her daughters and ex on FB and next thing i saw, MIL and SIL were mutual friends on ex's FB and friends with ex's mother. Ex even sent my husband a friend request which he hasn't accepted and has no intention of accepting her friend request. I thought to myself, how awkward, has anyone ever experienced anything like this? because i would really like to hear about it. Yeah is it normal for MIL and SIL to be mutual friends with ex and ex's mom??? and Ex sending husband a friend friend request??