I need help with finding our what movie is this? I really can't find out and I don't remember much of the movi?

The things I can remember is that a guy lives with his mom. His mom
meets a guy on her work and they get it going. The main character
dosn't like this guy etc. He also falls inlove with some girl that has
a fling with a teacher or something.
If i remember correctly it ends with that the main character rides the
bus to somewhere and the girl he is inlove with follows in her car.
She catch up with him and then I can't remember more :p