I've started daiting my SO about four months ago. As soon as we met he told me he had a daughter and that her mom abandoned them short after she was born. That little girl is so sweet I love her already. Everything between us as a couple was great I fell for him so fast. But, when I asked him if he had a Facebook account he said he didn't, he said that he deactivated it a few years ago and I believed him. After that, I looked for his sister on FB and found out that he actually had an active account and his profile pic was a little boy, so, I obviously freaked out and immediately asked him why he lied about not having an account and who that little boy was (that boy looks just like my SO), he told me that the boy is his son and that he didn't tell me because he didn't want me to think he was going to leave me and was using me to get over his ex (the boy's mom). And after a lot of conversations I forgave him for hiding the fact that he had a son. 

Now his ex is telling everyone that she still loves my SO and wants him back, she has been calling him a lot and she's telling people that they're hanging out. He says that she's crazy that he hasn't been seeing her and that he wants to be with me, Idk what to believe anymore. The other day he received a text from her and he freaked out and put his phone away. 

Any advice???