No judging please!

Danielle
Me and my partner have been together over a year now, we have known each other for 20 year. We are currently expecting our first baby together,only thing is, he is sill married. They have been separated for 3 year but haven't got a divorce yet. I thought I was ok with it, but lately she has been txting him for no reason, asking what he is upto, how he is n stuff. (He always tells me, doesn't hide it) and even going as far as liking our scan photos and things of our baby on Facebook, it is really getting to me. Am I just being stupid and over reacting? They don't have kids together so no reason to be in contact. I have also been getting messages from a fake profile telling me to leave him, and he will cheat on me and im not his 'type'. I'm convinced they are from her. Do I have any right to tell him to stop talking to her? Am I being paranoid. I really need people's advice, not sure if it's just hormones. Thankyou