Made A Mistake & Need Help

i made a mistake a couple months ago and kept it up til about two months ago and i use to make reasons to back myself up and think i had good reasons for my actions when in all reality it didn't matter what i thought. (fyi my mistake was going after a guy who had a girlfriend. he said he was miserable, couldn't stand her, etc. basically the normal speech a guy will give you. but he made me so happy without even trying. he drove me crazy sometimes but he literally meant the world to me at one point. i regret going after him like that but it taught me lessons as well so.) either way, i can't take it back but i get headaches and feel sick to my stomach bc of the guilt. (fyi whether she wanted to accept an apology or not, i still thought she deserved one so i did apologize) but i'm making myself sick over this stuff. help please, it's been two months of feeling sick bc of this issue. (i'm in high school just fyi)