My girlfriend of a couple months was going to go out with old college friends. All female and one male. I asked if she ever messed around with her college friends, this one in particular. She said no she hadn't. So I'm ok with her going out with them. Well turns out the plans were cancelled and she spent the day with me instead. A month later it comes up and I found out she did mess around with him in the past. Just one time and not sex. She tells me she said she never slept with anyone of her college friends. Technically she's right but she should have mentioned it anyways. Now she says she got a text from him wanting to spend the night. She didn't mention this until then. She said she lied to avoid a problem, but it created a huge one. What should I do?