Ask him outright and then delete him and move on. Could be tons of reasons.
My partner had gotten caught up in old childhood crush feelings with his brothers girlfriend. She was quite happy to leave and start a new life. He decided he didnt want to because he didnt want a partner who would cheat, he was embarrassed to be seen with her and the biggest reason - he realised what sort of person she was which smashed the rose tinted glasses hed had on for years and he simply didnt like the real her.
She cant accept this of course and pretends its somehow my fault shes an intolerable arsehole that no one wants to spend time with (her partner literally leaves early every morning and eats breakfast in his car because he cant stand her. One of the reasons she uses for cheating on him)
Made lots of public comments about my body and genitals, how I'm just a better shag, do more in bed, younger in better shape.
The fact is I'm a better person. I don't do the horrible shitty things she does to people. I dont spend all day screeching at my kids. I dont threaten, lie, blackmail or manipulate. We have more things in common. We dont struggle for conversation because I dont spend my life causing drama with the school mums, rehashing every bit of the drama interspersed with yet another repeat story about labour and childbirth to maintain my position as biggest martyr.
The fact might be hes realised he doesnt like you.
Stop stalking his life. Ask him outright why he broke up with you. Then learn and move on.
He could just be a scumbag who gets bored after "the chase" and moves on to the next pursuit. But no one can tell you here and constantly stalking them isnt healthy. We ended up getting a restraining order on her.