Lyric discussion by Jonnyxx 

Cover art for Jonathan David lyrics by Belle & Sebastian

BandS played this song at Reading Festival this year and got a random girl out from the crowd to dance along. They introduced the song by saying one of them would play Jonathan and one of them would play David and they were fighting over this woman. during the song whichever of the guys wasnt singing would dance with the girl but at the end as they sang 'married and you'll be gone' Stuart (Jonathan) and the girl ran off stage. It was very theatrical and nice.

so that definitely supports Southbound's interpretation.

great song.