Why do they monkeybranch then come back?

Mine pretty much emotionally cheated chatting to a girl who was pursuing him now she was single and from his past. Started pushing me away but wanting me to stay over and got new bedding because I said his was too hot and wanted to show me then ghosted when he monkeybranched. Then when I’d started to heal came in pretending nothing had happened after ages.

I’ve left him on read each time (why would I reply to replies to my story and no acknowledgment) but don’t get why they come back if they have a social life. Like meet someone new. If you weren’t good enough for them to stay it’s not worth it.