I know Clark is answering from his point of view, but I guess this is my take on it too since some of this is directed at me as well. I think for us it has been easier in a sense that prior to our new adventures, we were still in a very happy state in our relationship. Yes, of course once you've been together for as long as we have, you end up developing, let's say, "favorites"... But we've always made an effort to devote energy to our relationship. We try our best to keep "dating" each other
I would say if anything we have the opposite situation, I'm the one telling him if he doesn't stop harassing me for 10 seconds, then dinner is never going to get finished and we are both going to starve to death haha. So no, for us this isn't an issue.
For both of us, our first preference is to have the other involved, rather than being one-on-one with a new party. If I feel like he would be bothered by something, it is actually a turn off for me... It's not a trust issue, it would be more of whoever hypothetically was going solo with a new party being too worried about the other to enjoy the experience. So it's not so much that I would be uncomfortable with another woman, but I would be uncomfortable just knowing there was even the potential he wasn't thrilled about the situation somehow. Even if his involvement was just watching, I like having the reassurance that he is enjoying what is going on.
As far as civilians go, unless we were participating in a very particular type of event, we don't necessarily go around just checking everybody out. If we are going out on a date together, we are probably focused on each other! We do talk about celebrity crushes though, especially if we happen to have any ladies in common