I doubt he'd ever do anything really bad, but I know if they did break up my sister would hold a grudge(she's a great person but takes breakups pretty hard.), and it would certainly make things extremely awkward between us, at least for awhile.

I'm just glad that so far there's no indication that they will get to that point. They are pretty good at communicating with each other and they already have a system in place that keeps finances from being a point of contention between them, so the most common causes of a divorce shouldn't be an issue short of something drastic happening, like my sister or him developing a disability that keeps either of them from being able to work.

It's just concerning for me because my entire social circle was basically formed thanks to their relationship. Every other friend that I am not quite as close to I met through them and they are closer to him and they are with me, and I know at least a few would sever connections the minute they got divorced as a show of support for him, even if he asked them not to, which knowing him he absolutely wouldn't want them to.