Dear Tumble - I am reading your post at 03:34 (I hope you got some sleep) and it reminds me of your first thread, where you acknowledged that you did not challenge him on things for fear of being like his ex.
The post is about everything you did to keep him happy, and still he went back. What about you? What made/makes you happy? This was a man, from what you already knew, had not taken his children to his own place, saw them at his ex-wife’s, texted a lot with her, paid a pittance in child maintenance, gamed a lot of the time, has a poor work ethic - not sure, might have missed something - and you bent over backwards to make sure he didn’t go back to her (rather than saying, she’s welcome to him). In the nicest possible way, I think you were hoping he would be/provide the family you lack, except he already still had his foot under the table in his first family.
This is on top of a fairly traumatic-sounding life to age 22, with no maternal support, an abusive ex and a child you are not primary carer for (I respect your right not to discuss this, I am just saying how much you have come through)
At the moment, however hurt you feel, you do have a nice flat, a good job to return to, your DS with you, your aunt who sounds supportive, and your whole life in front of you.
This is why posters are saying stop engaging with your DS dad, his ex and extended family. It’s ‘enough’ time. Take care of yourself and your DS. Just stop, take a deep breath and get on with the chance you have for your own life.
DS will have appropriate contact with his dad, if dad asks. That is the end of your responsibility to this man.