just for me, so I am quite limited in what I can do. But in other ways, you've got a lot more options.
I've done quite a few city breaks on my own - train to airport, cheap flight, cheap single room - and then just do my own thing. I've also done various long weekends round Britain, and I'll be going up to Liverpool later in the summer over a couple of days, mainly to see the Chagall exhibition at the Tate, but I'll fit in other things round it. I've booked a yoga holiday later this year, which is something I've never done, and I am mildly terrified by it, but less terrified than the thought of driving myself for long distances would make me (I can drive okay, but I wouldn't count long distances of it as any sort of holiday, as I don't particularly enjoy driving.) About 12 years ago, I crossed half Africa on a truck with a load of strangers. I've had friends who have done things like cycling holidays, where they take your luggage, and there are other activity holidays you can do, which are geared up for single people.
Travelling alone can get wearing (just stuff like having to take /all/ your bags with you to pop to the loo or something), and there are some things I won't do because I'm on my own. OTOH, there are probably some things I've done because I don't have to consider anyone else when making decisions. And I know that if I don't make myself go away from time to time, I'd be even more depressed, because I'd just be at home all the time, on my own, all the time. If I hadn't done all the things I've done on my own simply because I was single, I'd have hardly ever gone anywhere or seen anything or done anything. It really can be worth the effort, and there will be something out there, either in Britain or further afield, which will suit you. (And it doesn't have to involve driving unless you want it to.) I know it's hard, but sometimes, making yourself do it really is worth it.