I acted in high school plays and recall just one stage kiss. The director told the kids to make it just a quick peck, no big deal. So back in high school drama we were never taught real adult stage kisses, and I'm thinking you didn't learn how to properly stage kiss back then either. Stage kissing isn't like movie kissing and most non-actors replying to you here are probably imaging all the steamy movie kisses they've seen.

Has you wife learned the techniques and protocol for stage kissing? If she doesn't know she could probably find videos on youtube that demonstrate the techniques. It many cases they only need to simulate real kissing so it looks real to the audience. There are no tongues or open mouths. Their lips might not even be touching, they kiss to the side of the mouth or creatively block it.

I think it's reasonable to tell your wife you're OK with kissing on stage if it's a stage kiss and not the kind of kiss she'd give you (or would be expected of her in a close-up movie shot).