They were invited by a mutual friend to come over and shoot skeet. (Marcus got to show off his skills, and Bethany ignored him all night). The next time that friend was having a get together at their house, Marcus came intentionally to spend more time with Bethany. She crashed her car on the way to the house that night, which became the talking point that helped Marcus get her number.
Marcus took Bethany to her favorite restaurant, watched one of her favorite movies with her, then took her back to the college campus and played their song before proposing. Marcus was so nervous the entire day that he kept accidentally dropping hints towards the proposal, and Bethany still jokes about it.