You may have a point that your feelings stem from mistrust of this woman. I don't blame you; pushing for no-condom sex outside of an ongoing relationship is, well, stupid. I recommend two rounds of paperwork first, 6 months apart, for all partners and meta-partners.
But you also trust your husband. He sounds reasonable.
I would tell him how you feel, being careful not to present it as "I don't want you to do this" but as "I'm just checking in, reporting where I'm at, but you go have fun, I'm dealing with my jealousy."
The anticipation is almost always much worse than the reality. Make plans with yourself to have a good time while he's away, and then see how it goes. Re-evaluate from there to see what you need next.
Gralson: my husband (works out of town).
Auto: my girlfriend (lives with her husband Zoffee).
The most dangerous phrase in the English language is "we've always done it this way."