The answer, very simply, is "You can't be sure." As you are discovering, people can be selfish and hard to get along with, and your next situation could be just as difficult if you make the wrong decision.
But don't misunderstand me; I'm not saying it has to be this way. The reason is because God loves you, and when you put your life into his hands and seek His guidance, He will help you make the right decision. He will also help you get along with people who may be difficult (even your parents!) because He will give you a new concern for others.
Elsewhere in your letter you admit that you have never thought about God very much or wanted anything to do with Him, and I appreciate your honesty. You even admitted that you wondered why you were writing someone like me! Could it be that God is trying to get your attention because He doesn't want you to keep making unwise decisions? I believe so.
My prayer is that you would turn to Christ and ask Him to come into your life and He will. You need His forgiveness, and you need His wisdom for the future. The Bible says, "Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make your paths straight" (Proverbs 3:5-6). This is God's promise to you.