I have strep throat, but have been on antibiotics for a day. Can I kiss my girlfriend and not give it to her?

No. You should refrain from oral contact until you have finished your course of antibiotics. The purpose of the antibiotics is to sterilize the oral cavity and it's appendages. Just don't do it. Why take the chance of giving her strep throat or even consider the fact she could give it back to your and you have a circle of infection going on. Harness your hormones and hibernate!