Thank you everyone for your responses. Shortly after I posted this, we met up and I said, as concisely as I could, that I wasn't ready for a relationship. I think they were caught completely off guard by this and there was some crying (from both of us). I gave them some time to process it and we subsequently met up a few days later to talk through a few more things. Initially I was concerned I'd lose another friendship, but it seems that we've managed to move past it. Obviously I have no idea how they truly feel, but we still see each other a couple of times a week in social situations and we still talk on and offline (not excessively, just a regular amount). At the moment, perhaps as a result of being honest and prompt with my feelings, things seem to be going ok.

I suppose that, now I've announced it's going well (even if only to a bunch of strangers), things might suddenly start going wrong, but that's just the way life goes sometimes, isn't it? I made a decision, I believe it to be the correct one and I'm sticking to it. Personally, I do feel better for having said what I did and I hope things can carry on as normally as they were before.