I can't decide if i want to be with someone who lies to me.

I've been with my girlfriend for a little over a year. This last Friday she went out for a couple of hours with one of her good girlfriends. She told me when she got home that night some guy at the bar came up to there table and talked to her. He said he was new in town and he wanted her to show him around town. She told me he tried giving his number to her but she said she had a boyfriend. Anyways i didn't think anything about it. On Sunday i saw she added a couple friend requests on facebook. I confronted her about who this guy was and she walked away from me. Anyways i followed her and kept asking her about it. Finally she said it was the guy from the bar. I left the house bacause i was so mad she would lie to my face. Well later that night i found out that she didnt even mention she had a bf that Friday night. She said she was sorry about the whole thing and deleted him off of facebook. Im so lost on what i should do. I love this girl with all my heart.