my bsf of 4 years is also my ex of 12 days

i met a guy through a friend 4 years ago and 2 years ago we tried to date and it only lasted 12 days before we broke up. we stayed friends, but i never got over anything that happened between us. after we let someone come in between us and it led to a misunderstanding and also stop talking to each other for a year… he texted me again a few months ago and we’re friends again, and i still have a lot of feelings for him. but i know i’m not allowed to have those feelings. they feel illegal, they feel dirty, i feel like a bad person for doing this when he went out of his way to reach out to me ( i thought he would never do that ) and i feel really selfish for feeling the same feelings that ripped us apart. i don’t know how to cope, because everyone around me tells me im making a bad decision but if it were that easy to give him up i’m pretty sure i’d have done that by then. im saying all this here because ive tired out all my friends with this same situation and wanted to know if anyone else is experiencing the same thing… i feel so bad for betraying his trust like this but i can’t help it, my feelings never went away even while we were apart for that year.