I asked to know when things became sexual....because....well because for right now I need to know because this is a hard part for me and I want to deal with the emotions it brings up and be able to ask for the reassurances that I need.
I think in any poly relationship, or even just an open relationship, this is a no brainer. Whether we have complete trust in our partner or not (which you obviously do not with good reason), a sexual relationship with a third (or more) party needs to be told because it can and may effect everyone. We would hope and trust that our partners are using safe sex practices, and I don't want to judge your husband but do you know for certain that he is having safe sex with these women? Do you know whether or not the subject of being disease free/tested was even broached by him or her? These are all things that effect YOU as long as you are also having sex with him.
Personally, even though I trust Cajun completely, I would still want to know these things before he embarked on a new sexual relationship.
*edit: and by sex and sexual relationship, I mean anything from oral to vaginal to anal...everything