That question was addressed at length on a thread yesterday.
Bottom line: men sharing beds was no big deal back in Lincoln's day and had nothing to do with sex.
Even the Log Cabin Republicans agree: they don't claim he was gay, only that "he built the Republican Party on the priciples of liberty and equality".
You are right. I recently read a book about a person in the 1800 and it talked about the men sharing a bed when they went on trips.