Honestly? I'd prefer that authors avoid the Happily Ever After trope in general. I can understand both points; it's frustrating to have the whole "your first lover is your only lover" cliche since that's so rarely realistic, but it's equally frustrating to have a relationship tossed at you out of nowhere.

I suppose the random relationship one annoys me more, but that's because it might be rare that a first romance is the only one, when the pairing is set up properly, it comes across as heartwarming and touching. Childhood/teenage friendships turning to True Love isn't really a trope I care much for, but I have seen it done quite well. Usagi and Mamoru from the BSSM manga is one such example, or Sophie and Howl, from Howl's Moving Castle. You see the development of their feelings for each other and it feels very believable that they really are the one for one another.