basically they were pretty solid, the only real issue being that audrina kept their relationship under wraps from the very traditional grandparents that raised her. she brought the gf around the house but it was very oh yeah, me and my friend are going upstairs to study and oh yeah, we're going to the dance. you know, as friends because we don't have dates.
i figure this was bound to annoy the ex from time to time and lead to fights and maybe even the occasional break up but the ex ultimately understood why she couldn't be open about it (and audrina was open with friends, etc) and they sort of kept drifting back to each other and making up. they were pretty solid, but ultimately parted ways once they went off to college because of distance (and i figure it was pretty amicable and mature with them knowing they were about to be going through a ton of changes). i'd love for them to still be buds and sort have rekindled their friendship when audrina came back to town five years ago. this can obviously be tweaked in bits to suit your character and how you think they'd have dealt.