How do you deal with a relationship involving two VERY attractive people?

I have a friend who is very attractive, he is the apple of the eye of the local gay community. Six months ago he entered into a relationship with a man who is equally attractive. Over the last few months they have been entering into the committal stage. Moving in together, adopting a dog, and even getting close to the "I Love You" stage. But here is the thing, my gut is telling me this is not love and my friend is seriously talking about marriage. The thing is both these men are "golden boys", beautiful, white, and young. They have not heard the word 'no' in a long time; life has not given these men the tools to form a serious relationship. I've discovered that I'm not the only one who thinks this several of our mutual friends have brought up the same issue discreetly with each other. We have all seen this, two people who are clearly dazzled by each other's beauty to make sure they are making the right decision. Have you had this problem? How did you deal with it? How do you say something to someone that is clearly going to sound insulting but probably saved them from a lot of pain in the future?