Re: Can I get pregnant from dry sperm?
Sperm lasts way more than a few seconds after it hits the air, lol. Otherwise men wouldn't be able to make sperm donations, or have their samples checked for viability. They last for quite a while actually, but once the semen is completely dry, all the sperm would be dead, but that takes a while - definitely more than a couple of seconds.
As for the risk you took with your boyfriend, there is actually a risk because while the outside of his penis might have been completely dry, his urethra could still have had viable semen in it, which could have be released once he entered you, even if it was just half an inch.
I would consider getting the morning after pill.