Unconventional,
I ask this question because I kind of recognize where you are.
I do believe it's possible for someone to maintain a relationship with an affair partner without it becoming romanticized or leading to another affair. I've seen it happen when affairs result in children, where continued contact is necessary.
But I also believe it's unwise to maintain a relationship with an affair partner unless circumstances necessitate it, such as when children are involved.
I wonder if the question of, "Can I build enough protective walls around the whiskey?" might be the wrong question. Maybe the question is, "Even if I can, is this something I should choose?"
But I'm not sure there are only two options: having your wife's approval to have this friendship or eventually becoming resentful.
Perhaps there's a third option: choosing to let go of the affair partner because maintaining the relationship is hurting your wife. Even if someone believes they could be completely safe with their affair partner, they can still decide that protecting their spouse from further pain is more important.
That doesn't mean letting go is easy. It doesn't mean the attachment wasn't real, or that ending contact wouldn't hurt. But there's a difference between acknowledging that something is difficult to lose and deciding that it therefore needs to remain part of your life.
Maybe part of the struggle here is that you're trying very hard to solve something that may ultimately need to be grieved.
I think our minds are really good at bargaining with ourselves when we're hurting. We look for reasons why we might not have to lose something we don't want to lose.
And maybe, in the end, it's just grief over the closing of a chapter. That grief doesn't necessarily mean letting go was the wrong choice. It may just mean that the choice was painful.