How do you get over your fear of kissing in front of people?

Fears are different among individuals. The best way to get over a fear is to confront it head on - not once, but multiple times until you feel better in those situations. In your case, this is pretty easy. It's not like every person out there is a voyeur. That's a relatively uncommon fetish... People may look if it's something like a make out session, but they'll likely walk off after a few seconds. Just start out small with a simple kiss, and work your way up.