I need some serious relationship advice, involving a father meddling in our relationship?

Stay out of it! I'm not trying to sound mean, whatever happens shouldn't have to be your fault. 'Chris' and the father are the only ones that should be telling her, they need to tell her the truth themselves. If Chris hadn't told you, you would never had known, and you wouldn't be responsible for telling her anyways. What that father did was wrong,yes, but it's a touchy matter that could cause a lot of hurt. Give careful thought before stepping into it farther. I'm sorry my opinion is kind of scattered. If it were me, I'd probably tell the mother,just so that she knows all the facts and decide what to do. But I can't reccomend that course of action mainly because it could backfire in so many ways. Just think a little longer. Make a pro and con list if it helps.