Marriage or Cohabitation

I know a girl who has been with her boyfriend for seven years. She is 24 now, both her and her boyfriend have their careers, and she really wants to get married. They live together and she makes her desire to get married very obvious, and she has for a couple years now. I think that in his opinion, it's like they're already married, so why should they actually take that step. I think this becomes a huge issue when couples decide to take the step of cohabitation, and for this reason, along with others, I would not endorse cohabitation before marriage. My boyfriend knows this very well, and when we were in Disneyland with my family, my sister told me that they were talking about the story above, and my boyfriend replied with, "Wow, Jess would not stick with me that long if that were us." Which might not be entirely true, but I think it is almost disrespectful, that the guy in my story doesn't respect what his girlfriend wants so badly. I know that a lot of couples do decide to live together before marriage. I was talking about marriage with a girl I work with. We were talking about how a lot of people we went to school with were already getting married, and her opinion was that was so crazy, because you would think they would want to live together first to see if they could actually stand living with each other before they got married. In this way, it sounded like she thought of it as more of a test before marriage. I still don't agree with this, and I believe that if you are dating someone for long enough that you do decide you want to get married, you likely spend a large portion of time together and know pretty much everything there is to know about them anyway. Considering that this trend of cohabitation has recently become more common, and divorce rates have also increased, wouldn't you think there might be some connection?