I'm 20 years old. I was in a relationship with a Christian guy for about three years and because of me, he broke up with me. The reasons are small, like I irritated him which he doesn't like. I didn't do it purposely, but it happened. Now I regret everything and want to be back with him. Please suggest to me what I must do to get him back.
Clearly your former boyfriend did not think that what you did was a minor thing. He broke up with you over your behavior. You can't take back the words that you blurt out without thought. "When there are many words, transgression is unavoidable, But he who restrains his lips is wise" (Proverbs 10:19). You can't completely erase memories of bad behavior.
What it comes down to is that you did not treat him as someone special to you. You weren't careful with his feelings.
I don't know if it is possible to change the situation. I assume you have apologized for you behavior in the past, but repeated the problem, so he is not likely to believe that you are truly changing this time. You may have to learn from this, find a new boyfriend and treat him better.