What do people do in London on a Saturday night?

What do people do on a Friday and Saturday night? I'm asking this question because my neighbors lights are always off Saturdays and I feel like I'm the only person at home on those nights.

I use to go out to pubs and night clubs sometimes but don't really feel like doing that and getting drunk and being out my face every weekend as it gets boring after a while not to mention what it does to your liver and with the NHS possibly getting taken away from us in the future I'd like to keep my health. I have no friends either so its pointless me going to a pub on my own because that would be depressing, but hey this is London surly there are plenty of things to do?

What do people do apart from getting out their face every weekend? I need to socialize more as I feel that I'm just going to die a sad old lonely man. I'm almost 30 and most people are married with kids at that age. How can I start living my life again?

any ideas?