There is literally nothing to be confused about.
You have been dating someone who can't be arsed.
He noticed that if he said nice things to you, you tended to just believe him, like a child believes her mother.
So, he just says whatever he knows you want to hear, and then you give him attention in return, and he likes that. He doesn't actually care about you and certainly doesn't want to stop pursuing other women, so, obviously he will change his FB however he wants.
You asked a question that interrupted what he wants to do (that is, pursue other women) - you questioned him about his behaviour. That annoyed him, so he is ignoring you, and when he replies, he basically dismisses what you said.
He is hoping you with STFU and let him carry on with his desires - which is, to have you, as well as probably several other girls, on the burners at all times.
Who cares what his mother says? That has nothing to do with anything.
Please stop using up your precious time on a guy who is spelling out for you, super clearly, that you aren't in any way precious or special to him.
There is nothing to be confused about. Unless you're doing that thing where you have already decided that you are going to forgive him/stop asking questions, so you're just trying to argue yourself into believing that he really does love you, or some such rubbish