Well...my AF has been married 3 times and who knows how many girlfriends he's had since the last marriage ended. My AXH cheated on me and they got married and cheated on each other. And, my AXBF wasted no time finding a new girlfriend after I left him nor in between breakups.
They don't like to be alone. You can't take it personally. That will rip you apart and you don't need the added stress.
I'm so sorry. Has your divorce already been settled? Is it too late to make sure you've claimed your fair share of the finances?