Now is the time to leave. You have already invested 4 years in a relationship that is not working. Don’t spend any more time trying to fix this one. It seems pretty apparent that this fellow is not even really in the relationship anymore, anyway, for whatever reason.
It will hurt in the short run, but in the long run, it’s better for you to leave now, and then spend some quality time with yourself. Enjoy your alone time, and spend time with other people who actually like you, and treat you kindly. Now is also not the time to try to get into another relationship. Give yourself 6 months to a year, to even think about getting into another relationship. Work on yourself, and your own self esteem, learn what makes you unique. Pursue activities that are enjoyable and important to you, and do some things that you’ve been putting off because you were putting your boyfriend first.
If you think or know that your boyfriend is being abused by his parents, tell him that he should speak to his school counselors and let them know what is going on. They are in a position to help him get out of that situation. You aren’t. If you think he could be physically hurt, you owe it to him to speak to your parents (and/or your own school counselor) to let them know that this fellow needs help.