loneliness

I have always felt comfortable in my own skin - at least by myself. Being an only child, I have grown used to, often, being alone. But rarely have I been lonely. There has been the occasional period, yes, where I have felt excluded from a group, or less than wanted within a social circle. But it is particularly rare that I cannot be content with my own company.
However, recently, I've become aware that I am not functioning well when left alone.
A certain habit in which I used to indulge (self harm) has of late developed in to something of a crutch, on which to lean. However, I feel my lexis is lax. The use of the word 'crutch' would seem to suggest that when times are particularly hard. this is something I reach to.
Yet I find myself increasingly drawn to this method of coping. For instance; in the next room, my two closest friends in the entire world are sleeping. I should be sleeping with them, but instead, I have sneaked into the kitchen, procured some sort of cake slicing device, and have been busy burying its corrugated metal into my flesh for the past few minutes.
Nothing has gone wrong. I have spent a more than pleasant evening catching up with my friends, and drinking delicious wine and fruity cider, but I am sat here, discussing my ridiculous actions and peculiar thoughts on an anonymous blog, and they are tucked soundly in bed. Why am I the odd one? Why can this lovely evening not sustain me?
I'm not sure. I'm not sure if I'll ever be sure. I'm also not sure what drives me to hurt myself after a rather long period of absense from this modus operandi.
But for now, it preserves my mental health. Even if it is only a short term solution.
So I suppose I can't complain about that.
What's a girl to do?