Speaking to the earlier part of your post, GaK, in my experience, this is the time they start to develop a sense of self-consciousness. It coincides with their realization that males desire them in a "naughty" way that most of them didn't quite realize earlier.
Perhaps this other part arrives a little later, but they do develop a tendency to view everyone close to them up to a current point in time as part of their "old self" as they try to set out and explore with new people. This might explain why the girls you met online were more open to getting to know you. Way back in my days of making online friends, I found the same thing to be true.
None of this is written in stone of course. Every girl is different, and not all grow up the same way.
There's a few strange years around that time in my opinion, but eventually they learn the ropes and who they are and it gets easier to be close again. At least that's been my experience.
Yeah, our love can often be described as bittersweet. Learning to accept the cycle of love and loss is not a fun lesson, but it does turn us into stronger people emotionally if we can learn to manage it. For the few relationships that stick around and morph into something different later, the pain is lessened a bit, but those are far less common.
The good news is there's always a new LG somewhere who'd love to know us:)