The most likely outcome is, charmingly, a hung parliament, the first time since the bad old days of 1974—the Conservatives will almost certainly win a plurality, but not an outright majority, of both parliamentary seats and the popular vote. (Britain's electoral system is nearly as broken and undemocratic as ours, as you can see from the Guardian's Tactical Voting Guide, which we really could have used in 2000. Having more than two parties, but not instant runoff voting, leads to mass confusion, apparently.)
What will happen then? Nobody quite knows. Likely possibilities include a possible coalition ally putting on a thick coat and wellies and sneaking through rain-soaked fields in the South of England, to avoid reporters; or David Cameron outmaneuvering an opposition coalition a la Canada's Stephen Harper-headed minority government. The latter suggestion comes from 538, where your boyfriend of two years ago Nate Silver, who's been projecting the election, is predicting a swing in the direction of Tarquin Fin-tim-lin-bin-whin-bim-lim-bus-stop-F'tang-F'tang-Olé-Biscuitbarrel, Silly Party. This is all very confusing.