Good writers have been ending their sentences with prepositions for centuries. The real rule regarding this grammar point is the same rule regarding all sentences: if it sounds awkward, don’t do it (in this case, end your sentence in a preposition). The rule “do not end sentences with prepositions” was an attempt, like many writing rules, to give inexperienced writers the cut-and-dried guidelines they so desperately wanted in order to write correctly “all the time.” Such rules ignore the fact that good writing requires the writer to make subjective judgement calls “all the time” (“Does this sentence sound okay with the preposition at the end, or not?”) and actually lead to bad writing because no one can write well if they try to remember dozens of writing rules while writing.
An anecdote that appeared in Sir Ernest Gowers’ Plain Words (1948) states that an editor once clumsily rearranged one of Churchill’s sentences to avoid ending it in a preposition, and the Prime Minister (who won the Nobel Prize for Literature), scribbled the following note in reply: “This is the sort of bloody nonsense up with which I will not put.”