Here is a possibility why that recruiter was acting in your best interest.
As a spouse, you actually get benefits. You are the next of kin, so if he gets injured, killed, or whatever, they have to tell you. As a girlfriend/fiancé, the army CANT tell you shit. Your best bet of getting information or visitation is based soley on his parents. You also get health care, reduced cost dental care, you qualify for more student financial aide, there are school grants you qualify for, you can shop tax free at the PX and commissary, and probably more benefits that I cant think of.
What if he get's orders to overseas? If you want to go with, you are going to have a very short window to get things figured out. I.e. Married, marriage recognized by the Army, and then begin the command sponsorship process. Where as if you were married, you'd just have to begin the Command Sponsorship process, which is long AF anyway.
The pay! As a married Soldier, he get's paid BAH and family separation. That is around an extra grand a month.
Now, I recognize that younger people with stars in their eyes have a much more romanticized view of marriage, however, many of us "older guys" have a more pragmatic view, and base the relationship over the marriage and literally see marriage as a piece of paper. So, when people like OP are asking if it's better to do before or after, financially I'd always say before.
Granted, this is if you are already an established relationship, you are 100% certain about getting married and just trying to select a date.