First, can you explain why you're interested in buying a new place with your SO when you already own a condo (that you live in)? Presumably since you bought it, it fits your needs, does it not fit your needs as a couple? I feel like being the sole owner puts you in a more secure position than owning property with someone who is (potentially) unreliable.
On the other hand, for some reason I'm not feeling as concerned as some of the other posters. I'm glad your SO is an awesome person in your eyes. I also think that it's fine if a couple has different strengths - you can be a really powerful force when varied skills are combined. If your SO is genuinely interested in being more responsible, I think it's worth a discussion on how you can help. I, for one, sometimes really appreciate when my husband keeps me accountable for certain things - a well placed 'weren't you going on a run today?' or 'Isn't your exam in 2 days?' can kick me in gear when I'm being a bum. On the other hand, sometimes those comments come off as nag-y and are unwanted, so tread carefully.
So could you discuss whether any of the below actions (just my suggestions) could be helpful, or come up with some that are?
1) He cuts up his cards and you watch
2) He gives you his CCs to keep away from him (like when I made my husband change my Amazon password so I could no longer stream The Good Wife ... I knew I had to stop, but couldn't commit solely via self control)
3) Input his cards on Mint where you can monitor ... perhaps knowing you see all can be good motivation
4) Make a budget together and meet regularly
5) Make it a contest in a certain category as to who spends less (maybe give him a handicap like in tennis matches) then winner gets a massage from loser?
6) Delay gratification by committing to a nice dinner at the end of the month together if you both spend no money on eating out (or are below a certain threshold)
7) Set up a one-in one-out policy for clothes .. declutter what you haven't worn in a year, get him to think before he buys anything new
8) Take turns planning creative dates that cost less than 10 dollars (or X dollars) to both get in the spirit of appreciating the free/inexpensive things in life, and rely less on expensive entertainment
9) Ask him to try a low-spending 'diet' for some short period of time ... no commitments beyond that, but maybe a good way to get him to realize you don't need to spend to have a good life
10) Be the change you want to see ... prepare lunches for you both if you want him to eat out less (and be more thoughtful when he does), invite friends for dinners in (instead of out) and do most of the prep work
I think also that you need to be really honest with him about how finances could potentially impact your future. It's true that if you guys have wildly different values and ideas on how to spend money, that could cause a lot of friction in the future. Problems like that tend to only get worse (or else they stay the same and you try to be better at bearing them). I just generally feel like honesty is the best policy, and maybe emotions/feelings will speak to him more than the cold hard language of finances. For instance, as a woman (and the more organized person in my partnership, with better memory and the one who does more of the social organizing) I have a lot of concerns about equality and how burdens will fall especially if we have children, so I talk to my husband a lot about that. And beyond the talking, it's both of us acting with our best foot forward that prepares us for big moves like that - ie, when he does an equal share of cooking (ok, more) and cleaning, and all that other stuff, his actions convince me. The words are just an additional layer that helps.
So talk to your SO and give him the opportunity to understand how you feel, how finances affect you, and to be the partner you need. If you haven't been vocal, since he isn't a mind-reader, he may not understand how deep your feelings go. To many people, his behavior wouldn't seem odd or unusual or particularly irresponsible -- he probably doesn't think he's that irresponsible. He may very well have the ability to change. Plenty of us started with quite a different head space than we're in now. Good luck and keep us updated!