Thanks for the responses so far!
@Eamonn McElroy No, we will not be married by Jan 2019.
@Carl Fischer He makes more W2 money (probably around $35k more for this year - I was a postdoc lol, just got a slightly better-paying job starting this month); he is just barely in the 24% bracket, while I am in the 22%. I also have some investment income - last year it was around $8k combined in capital gains, dividends, and interest income. He has joint custody of 2 children from previous marriage and I believe he gets to claim one of them on his taxes. I have student loans and will have interest from that to deduct (if I itemize??)
This is the first year that we have really commingled finances at all - last year we lived together in that old house, and he just paid me a certain amount for "rent" and bills. Now, the rent from that rental is deposited into a joint checking account and the rental income above the mortgage and percent saved for expenses goes straight toward the mortgage payment on the new house - so we basically split it, and split the rest of the mortgage, utilities, etc. We still have mostly separate accounts and credit cards, etc.
The general agreement between us is that we are in this together - splitting profits and expenses according to relative income or evenly (mine will soon be closer to his) moving forward, but not completely commingling all accounts just yet (I have a lot in investment accounts from an inheritance - I also have a lot of student loan debt). We hope to work toward financial freedom - building some real estate investments is part of that (also likely doing a live-in flip on the new house). I did put more into both fixing up the old house and down payment and remodel costs on the new house, because I had more money available in savings.
Fiance also has a small business - I believe it's in an S-corp now, that he usually does not take income from, but they did do a payout last year which he used as part of the down payment on the new house. He has a lawyer and a CPA that's he's used for that business, so we have talked about talking to them about the real estate stuff, but have not yet done so ($$$). In the past, I've always done my taxes myself with TurboTax and more recently TaxAct, because they have been pretty simple, but I know this year will be more complicated, and I don't even know anything about depreciation except that it's a thing I need to do.