@Burnedbeyondbelief
He sounds like a narcissistic twat.
The triangulation, the lovebombing, then devaluing you, hoovering, blameshifting and gaslighting etc. etc.
I can see absolutely no redeeming features about him op. You say his GF gets everything handed to her on a plate, well that won't last and she will come to know what sort of person he is. He is playing and using you both as ego boosts, and manipulating your emotions.
He pops in and out of your life like a game of peek a fucking boo, whenever he wants because he wants to know whether he still has you under his control.
You are still in the fog and possibly trauma bonded to him, but well done for ignoring his recent attempts to get in touch with you.
Remove his contact details and block him on every platform to remove any temptation to reach out or check what's going on in his life. Block his GF on FB too.
You need to heal right now and that process will only slow down with reminders of him.
You are not the problem. You are enough on your own and do not owe him anything. Men like him enjoy tearing a woman's self confidence down while they are put on a pedestal. They do not deserve your time and attention.
It will be very difficult right now, but you will be able to see later that you were far too good for that prick and you have had a lucky escape.