I found out what happened last night with my girlfriend and I don't know how to handle this?

Just be supportive and be there for her. Maybe being at your house may not the best idea, with all that teen lust, it may make both of your parents uncomfortable and her father more upset. I would suggest going to her house with her, preferably when her dad is not there ( and if he is maybe take your with you guys) pack up some of her stuff, and have her stay at a close girl friends house. That way you will feel better because she isn't in her house, and she will have the support she needs from you and her friend.