To be honest, how likely is your partner going to admit to it even if he did? I would just watch very carefully for his reaction but before asking him i would try and weigh up the facts very carefully and try and get more information from your daughter if you can. Remember it was probably pretty difficult for her to tell you such a thing - regardless of the motive - so try and be as mindful of her feelings as you can. Some of the questions i'd be asking myself are along the lines of whether or not the divorce was amicable or whether it affected her more negatively, how did i play a part in that, how has our relationship been since? etc etc. It's best to be honest with yourself before you attempt to tackle this further.

If your relationship has always been fraught with difficulty and made worse by circumstance then i would be somewhat suspect but to be honest - why would she be trying for even more advantage now and in such a way? Was there a particular reason you were visiting her? You leave out rather a lot of detail so it's difficult to try and interpret your post further but i suppose the bottom line is whether this would be enough of a reason, if it could likely be judged as true, to leave your partner regardless of your relationship with your daughter and how this new issue might impact upon it.

Abuse is abuse and even if you're not sure just how much you want her to factor into the rest of your life, i know that if i were her mother i'd want to take some accountability - especially if she was still a child, in getting to the bottom of this. I wish you both the best of luck, there's no easy way to deal with this.