Is it reasonable to worry about lack of potential for dating in postdoc positions? I am 25 years old, and in a few months' time I will have to decide whether to get a job in London or apply for a postdoc somewhere. 

Apart from all of the usual pros and cons (eg. job security, salary, lifestyle) associated to each path, one thing that worries me most is my loneliness. I am worried that if I were to get a postdoc (say at some small university in some small city), that I would never meet someone to date and get married to eventually. Most math postdocs tend to be male (I believe) which is fine for me since I am gay. But it seems to me more likely that I will find true love taking a city job in a metropolitan environment where there are many more people. And I am really not sure that the "single life" is amenable for doing a postdoc in a foreign country (where I'll likely have to look to find a postdoc in my field).

I apologise if this thread is not suitable for this board, but it is an important consideration in a potential academic's life. I would truly appreciate your thoughts and experiences.

Edit: I guess I am asking whether I am right to be worried about the lack of potential for dating in a studious and bookish environment like academia, and whether anyone has any advices about how to deal with this.
How is Academia different that any other job? You work for a number of hours a day, and then you are free to use your time solving jigsaws at home or socialising with other people.

Perhaps the academic environment has the advantage of multiculturalism. In most industries, the large majority of the people are from the country; but at universities you can find much more diversity, and thus, easier to find people you feel more comfortable with.

Lastly, in large cities there are, statistically, more potential "suitable partners", but they will be more difficult to find. As a mathematician, you may want to model it as an Erdős–Rényi graph, for the fun of it.

In the end, I think either path will have comparable a priori chances of finding love, so this should not be your main criteria to decide what to do with your life. Being happy with what you do will make you a nicer person, and have a larger impact that the city you are in.

And, to put at ease your concerns, most professors I know are married, and they certainly went down the postdoc path.