Since we were still at the other house where his drunk uncle lived, he started to give me “affection” in hurtful ways, started with tickles, that at first were ok, but later the tickles became a form of punishment,
…and…
Then the biting started, it also started as something cute, but then he started biting me harder and harder, and then started to do it as another way of punishment.
Healthy relationship do NOT contain forms of physical painful punishment.
I kinda feel trap because I still love him and don’t want him to be depressed and die, but I’m not sure I can stay here
This is by design from him. Its emotional blackmail. You are NOT responsible for his actions, only your own. Don’t let him convince you otherwise.
He started crying, got very emotional, and finally agreed to go to psychology.
I think it would be a very good idea for you to go by yourself first. There are some very important things you should hear from a professional about their assessment of your current state and guidance for what to do next. Do this very soon.