Questions: Break Up & Divorce

I haven't talked to my ex in four months since our failed attempt at being friends after we ended things and a few weeks ago he sent me a random snapchat of him and a girl.

Through her social media I know its a new girlfriend. I didn't respond because it seemed pointless.

Two days later he sent me another one, completely random of an animal.

He was my best friend and I've never been so close to a guy before. I know I was one of the most important people in his life and at one time he thought I was the whole package and that he's never connected with someone or been able to share as much personal stuff with anyone before as he did with me, including his ex girlfriend of 4 years. The loss of friendship was hard but overall I'm at a good place and if he's happy so am I.

He seemed nonchalant about our friendship ending and that he "knew it wasn't possible for things to go back to normal," so I just don't understand what that whole thing was?

Perhaps you have trust but it still crosses your mind.

Maybe something your partner says or does makes you wonder.

Maybe you have been cheated on and have trust issues.

Maybe you don't think anyone would ever cheat on you!

Please explain all!