Guy's Behavior

Why would my Ex add me on fb but not reach out?

So I’m seriously considering un friending him and possibly blocking him as well but wanted to hear your guys’ opinion on this. Me and him were together for two months Sep-Oct, we were amazing together, and he all of a sudden became distant and cut off all communication with me without giving me any explanation whatsoever, which completely fucked me up for a month or two. Then I found out he started going out with another girl shortly after that happened, although I believe he liked her while dating me as well. Long story short in January she adds me on Facebook very randomly one day (we know each other but we never hung out and have 0 contact) and then few days later my ex sends me a request too which I for whatever reason accepted. He watches all my stories but he never said anything, no apology no nothing. He used to watch all my IG stories as well until I deactivated that in December. So I was wondering, how would you interpret this, why would he add me randomly one day after basically leaving me without even telling me we’re ending it, not talking to me for so long and then not even reaching out after he adds me? I don’t even know if them two are still together, I’m not a revengeful person nor do I want to have beef with anybody but now I’m seriously considering unfriending & blocking this dude smh.
(before anyone jumps telling me to move on from him, I did lol😂)
Why would my Ex add me on fb but not reach out?
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