He’s an irrational spender because he wants to own a house because he believes that homeownership says something about him (possibly “adult” or “success”) rather than because it is a good economic decision for your team.
It doesn’t mean you can’t love him or be his partner. It does mean you should treat his finances like a bomb that could explode any minute.
I think it just means “home”. Even I think that. But that doesn’t = “must do” for me. Which is why I’m here, talking to you fine people. 
I pretty much agree with this. If you want to finance a home purchase without the SO’s property/credit being a factor: take it out of the equation, and buy a house YOU can afford regardless of his eventual contribution, which sounds kind of iffy to me anyway.
Lots of good advice already, but here’s my two cents anyway.
The first thing you need to do is work out your current situation accurately. Set aside an afternoon to sit down together and work out exactly what you both own and owe at the moment. Make a little spreadsheet and add it all up. Ideally you should be working off bank statements and loan balances. Be liberal with the expenses and conservative with any valuations. For example your car is probably not going to be worth anywhere near what you paid for it, so don’t put it down at that figure in the assets column.
Then work out your cashflow - how much do you each bring in in a month, where does it go? Again try to be rigorous - get your pay info from your payslips, and your expenses from your bank statements. The results might horrify you - “We’re spending this much a month on eating out/gas/smokes/drinking!” but at least you’ll see where the money’s evaporating to.
Once you can draw an accurate picture of where you financially are you can discuss where it is you want to be. When we decided to get serious about buying a house we worked out a budget and started to set aside the difference between our current rent and how much we thought a mortgage would cost. Depending on your situation this money you put aside can be used to pay off the outstanding debts you have, or if they’re cleared you can start saving up for a deposit.
That ended up being our deposit, and got us used to the debt payments when we finally bought a house (just moved in this month yay us!). Took us a four years though. It kind of sucks having a debt again now, but in just under 15 years it’ll be paid off.
Yeah, not to beat a dead horse but the stats are out there. #1 reason of divorce is wildly different spending patterns, roughly translated, “differences about money”. #2 is different expectations between the sheets, and it’s a distant second.
Best case scenario, the frugal one keeps the spendy one in check. ((My mom had to teach my dad how to window shop, comparison shop, grocery shop…)) But…you need to start holding him to your standards before you marry and merge finances.
Otherwise we’ll get a thread in 2.5 years “How can a man with no job get alimony payments!?”
Thanks all for the suggestions. Planning on a financial advisor, realtor consult, and a bunch of reading/research. I’m pretty savvy and SO and I are on the same page about wanting to move forward in the right direction, and this is just the starting place. I don’t expect you’ll see any alimony threads, much as I know you folks like to eat that up! 