When I think about my social sphere, I'm seeing that it is difficult to go beyond 3-5 years in a relationship and not have at least an engagement in place.For my friend with the 7 years with the same woman with no marriage, the sex frequency has dropped a lot.
The guy who has gone 7 years in a relationship with no marriage and no immediate indication of marriage is somewhat unusual. They moved in together around the 3 year mark. He wanted to do it sooner, but she postponed it about a year or so. They are renters though so it would be less complicated if things ended now. She's more unconventional about marriage and family than he is. I don't think that's a situation that most men can duplicate. That relationship has also gone down in quality since they moved in together. I often wonder why that's still going on. Inertia and laziness have something to do with it.
I know another man who got to 5 years in his relationship with no marriage. He moved in with her at the 5 year mark, proposed marriage 6 months after moving in, and then got married around their 7 year point in the relationship. They've been together 10 years and married 3 at this point. The most fun points of that relationship are long in the past. I think part of the reason he was able to go as long as he did without moving in or proposing is that they met around their junior-senior years of college, which is roughly age 21. Once they got to the 2nd half of their 20s, it was all about marriage, dogs, and planning to start a family (hasn't happened yet).
There's something I noticed that has happened with couples around ages 26-32 in bigger metro area when they are childless and the participants have a BA/BS degree or higher. Weddings start happening in flurries. There's other anxiety and unnerved feelings around those who aren't married when the marriages start piling up, which can often lead to those on the later end of the timing spectrum on marriages to get into bad marriages due to feelings of immense social pressure.