I think sometimes it's hard to see just how far you've come, how much you're put up with and how well you've learned to deal with it. Then, when you tell someone of your past/hard present, they wonder how to respond.
I know someone who can be a bit angsty sometimes and, after I'd told him my history, he said he felt a bit awkward and didn't know what to say. He said he wished he'd not complained about his own life. Thankfully he's got an excellent brain in his head and is a total cynic, so can deal with what I told him, but he still said that he thinks his life has been sitting on a cloud and eating ice cream compared to what I've been through. We left it there and we've got on just fine since then, but I can imagine some feeling too awkward about it and wanting to backtrack out of the friendship.
I've kind of got used to not mentioning my history, unless it's relevant to the discussion. It does tend to leave people a bit shocked.
But then, I don't think that leaves me (and I hope not you, OP) lonely or anything, it just means you're effectively moving on, if you don't tell them about your past. It can be a healthy thing to do.