Ex bf acting strange?!..?

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My ex emailed me a few times but I'm not sure why or if I should continue speaking to him. He left about 9 months ago. Started dating someone else right away. We were together for 8.5 years & have known each other for about 16. He has never once stated anything regarding our relationship in the emails. The first one said he had a nightmare about me and wanted to know if I'm ok...?? The last one I waited over a week to respond & he responded right away at 3AM! I haven't spoken to him since he left till now.
I even changed my number I felt soo betrayed & hurt. I'm confused & cannot be friends with him. Ugh...??
Then today my sister tells me he's liking things on her Facebook! Their not even friends on there! Wich means he searched for her & liked whatever he could see... What the efffff..? ( He blocked me then recently unblocked me) This is someone who completely pushed me out of his life months ago.. Help!