He's an adult with a college degree. He should know better. Has he actually asked your advice? If he does, be honest, but if he's just complaining, be supportive but don't offer your opinion where it isn't wanted. I would probably rib him a little about the change in his ways, which could prompt a more serious conversation, but likely he realizes the truth. When he wants to admit the problem, he'll address it.
I can honestly say that the single smartest financial decision my husband and I have ever made was . . . each other. Choosing a spouse with similar financial values has avoided so much heartache over the years. Thinking back to guys I dated before my husband, how they handled finances was definitely on my mind. The first guy I dated seriously just couldn't handle money -- he had more than I did, yet by the end of the month, he was borrowing from me. I was young and stupid, but I remember clearly one day we were talking about marriage and our goals for the future -- and, yeah, I really thought I would marry that guy -- and he commented that "pocket money was a big priority for him", that he didn't like to walk down the street and feel that he could not stop to have a nice meal or pick up an item that he just wanted. This was so far out of my idea of "right" that I asked him to clarify. Yep, his answer was just as stupid as you're imagining, and it was a huge eye-opener for me. I started watching his spending at that point, and that really was the beginning of the end.
Money was an issue with the second guy I dated too. He did some dishonest swindling with his dad: He was able to "pretend" that his college expenses were actually higher than they actually were, and he was pocketing a couple thousand every semester from Dear Old Dad. It made me wonder how honest he'd be with me in the future. I did admire that he really did his homework when he made a purchase, and he never bought anything that wasn't likely to be used a long time -- I have those same traits.
When I met my husband, we went out frequently and spent money . . . but he loved to go to a restaurant with a buy-one-get-one-free coupon, and he liked the dollar movies. When we talked about money, he was interested /informed on real estate purchases, the benefits of saving early, frugal living. It was one of the things that made me think we were compatible.