I got a piece of open skin (hang nail that has blood marks - could it be microscopic tears?). touched sperm. hiv?

Very unlikely: Even a hangnail is covered with fibrin; this is why it's not dripping blood. If this is troubling you, or there's some other issue, give your personal physician a phone call. We're here to help, and we're not going to judge anybody -- we're heard it all before. You're almost a grown man. It's good that you're health-conscious but you can't be a cripple of unfounded fears, especially about loving.