Search Results: adding friend on facebook

My friend was in a rather short but somewhat serious? relationship with this guy for a couple of months. However, she broke up with him around 2 months ago, and since then, he had texted me letting me know that she (my friend) had been talking shit behind my back, along with our other friends, which I already somewhat knew, but of course he would try and get back at her and maybe this was his way of doing so, but all he said in the end was that I could do better and that she’s clearly not a good friend to me, which I already knew. Now, for other reasons, her and I have kind of been on the outs for a bit, and on one occasion she had snapped at me because I let her know that her ex was saying some that he entirely regretted his past relationship (without mentioning her name) on social media, which I saw because I hadn’t gotten around to unfollowing him yet. Anyways, she got mad at me and said “Tf I don’t even know why you’re still talking to him why would you do that” and so on, which wasn’t exactly the case at all. Anyways, a couple of weeks after that, a random account had written on one of my old posts with her and I in it saying “*my name* was always the hotter one”, and it doesn’t take a rocket scientist to put to and two together and figure that it was him who said that. Regardless, we ignored it. Now, he has sent me a friend request on Facebook. It doesn’t sound like much, but I kind of want to know what his motive is and if I should or shouldn’t add him. May I remind you all that I had been treated unfairly many time by my friend who is his ex, and I know that if she found out that I added him back/and or talked with him, that I would never hear the end of it from her. I’m not trying to steal her ex or anything if I add him back, and I don’t think he is going after me either. I think he’s just hung up on her or trying to see how she is. What should I do? Should I add him back? Should I start up a conversation with him and ask what he’s trying to do?