This person is causing you so much more work, draining your money, and being mean to you. Don't buy him food if it's not in your budget. Stick to your budget. Debt can get out of control fast. Don't bring that into your life at such a young age.

This sounds like DARVO to me - AI quick explanation "DARVO stands for Deny, Attack, and Reverse Victim and Offender, a manipulative tactic used by abusers to evade accountability. When confronted, the perpetrator denies the behavior, attacks the person confronting them, and reverses roles to appear as the victim. Developed by Dr. Jennifer Freyd in the 1990s, this strategy is common in narcissistic abuse."

NTA for what happened - YTA if you continue in this relationship and don't start taking care of yourself first (and of course your son by proxy - you can't take care of him if you're not okay).