Why would this guy delete me from all social networking websites?

We had a fling just over a year and a half ago now. It shouldn't have happened because he had a girlfriend. I developed feelings for him but we mutually agreed to end it after a while because we knew it wasn't right. His girlfriend never found out but we did stay friends and got in touch every few months or so and asked how each other were doing etc. The last time we spoke was via Facebook message about three weeks ago. It was a pleasant conversation and we said how nice it was that we managed to stay friends after all that happened. Yesterday I noticed he has deleted from his Facebook, unfollowed me on Twitter, and unfollowed me on Instagram. Very strange considering we were on good terms. I can only think his girlfriend found out something and told him to do it, which I understand if this is the case. I saw an Instagram photo of them both in a picture smiling on his account a few hours ago so everything seems okay between them... Hmm... What do you think is going on guys?

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