What is the Unitarian Universalism Churches stance on adultery?

I am UU, but today my Mom who is not (and doesn't get the UU thing) put me on the spot by asking what is the UU Churches stance on adultery? I could give no clear answer. Dad left her and is married to someone else, there was involvement between the 2 when my parents were still married but the marriage was beyond repair. I don't see it as betrayal because the marriage was dead anyways. Can someone give me an answer?