Someone asked me if I would be willing to officiate a traditional handfasting for her, one that would end in a year and a day rather than the legal marriage ceremony. She is married but her husband is fine with her being handfasted to another. Can anyone think of any legal or ethical implications to the ritual? I figure if all parties are okay with it, I should be, but I just don't want anything to come back and haunt me. Suggestions or comments?
I am not aware of the legal implications of a religious wedding ceremony in the US, so I can't comment on that.
Ethically, if all parties concerned have given their informed consent I don't really see a problem. If you are not sure everyone is on the same page, verify with all three together (preferably) or seperately (if you must). Customize the ritual to fit their request: to fast hands for a year and a day only. This is not as binding as "life long or beyond". Have their own vows, if any, reflect that. At any rate, all handfastings I have witnessed specifically mention that the priest/ess does not bind the people together, but they commit themselves to each other. You are only there to guide them through the process practically. I strongly recommend you incorporate that into this ritual as well. Should the relationship end, that is not your doing and it will not "haunt you".
A friend of mine once handfasted a couple without the woman's legal husband knowing, but he demanded they told him within a fortnight of the ritual and was present for that conversation, for his own peace of mind. The handfasted couple separated months later. These things happen, people and relationships are complicated sometimes. In this case, I don't think you are "meddling" or doing anything wrong.