I've been guilty in the past of (more or less) dropping friends when I've begun a romantic relationship. But they've always had other people for company as well....luckily there's never been anybody outside of romances who saw me as so central to their life that they'd be severely hurt if I were to be with them less often - at least as far as I know. The only exception was my son....when I got my own partners after separating from his mother he tended not to like it, but I made sure his needs came first whenever there was any contest, and annoyed one or two women that way.
But I've never completely closed the door on anybody because of a romance, apart from a rather promiscuous old flame who turned up when I'd found a monogamous relationship....it wouldn't have been reasonable to expect my new partner to trust her with me, though I felt quite bad about lettting her go.
As far as I can remember I've not been "dropped" by anybody for the sake of their romantic growth....there have been a few couples I'd have liked to have shared more time with but had to make allowances for their own commitments to each other and give them a bit of privacy. And of course when my son began to grow up I had to accept that my role there was in some ways gradually coming to an end - it hurt a lot, but of course there's no escaping it.
I voted "too complicated" for the "own best friend" thing. There are many ways in which I trust myself more than I trust anybody else, and I do have a lot of trouble coping with people, but I wouldn't want to be alone permanently...left in my own company I can start going round in ever-decreasing circles, so although I don't always like it, I need the input of others to give me a better view of myself and what I'm trying to do.