I just do not understand why so many non-Bangel shippers think B/A is immature or a teen romance.
Buffy and Angel IS an immature teen romance. But why is that Bangel supporters feel that they have to get defensive when that is mentioned, or see it as necessarily derogatory, condescending, or an accusation? Speaking strictly for myself, I've called Bangel all of those things, but I've never once seriously said or implied that it wasn't at the same time sincere. If we're going to be asking "Why is it?" questions, why is it that so many Bangels seem to feel that either Buffy or Angel is incapable of ever loving anyone else? Monster or not, Angel is just as human, emotionally, as Buffy, and both are fully capable of loving more than one person, romantically and equally, but in totally different ways.
Angel loves, and is in love with, both Buffy AND Cordy, and I suspect that, if the series had lasted a few seasons longer, he would have also been in love with Nina or some other girl, eventually, just as Buffy was sincerely in love with Riley AND Spike, and might yet be in love with someone else.. That's how love works. Yes, Bangle is special, VERY special, and absolutely necessary for a very important reason. It's first love, and without first love, there can never be second love, or third love, of twenty fifth love, if someone lives long enough,the way that an immortal being like Angel could.
Buffy and Angel may, if Joss ever decides to allow it, end up in as close to a "happily ever after" relationship as the Buffyverse ever has, but if they don't, if one or both of them end up with someone else, that in no way means that, actually, for all these years, they never have really loved each other.