Im a homeowner cost sharing expenses (Mortgage, HOA, Utilities, etc) in half with my significant other. What changes when I file taxes now vs when I was single last year?

Then you do not report the "income" from your SO as rent, nor can your SO claim rent credit if you are in one of the states that has such a credit.   You simply enter your home ownership amounts on your own tax return.  They may or may not even make a difference.

Go to Federal> Deductions and Credits> Your Home to enter mortgage interest, property taxes, and loan origination fees (“points”) that you paid in 2022.  You should have a 1098 from your mortgage lender that shows this information.  Lenders send these in January/early February.

HOMEOWNERSHIP DEDUCTIONS

It is very hard for a lot of people to use itemized deductions now that the standard deduction is so much higher.  Your home ownership may not have any effect on your tax due or refund, especially if you purchased the house late in the year.  

Standard Deduction
Your itemized deductions have to be more than your standard deduction before you will see a change in your tax owed or tax refund.  The deductions you enter do not necessarily count “dollar for dollar;” many of them are subject to meeting  tough thresholds—medical expenses, for example, must meet a threshold that is pretty hard to reach.  The software program uses all the IRS rules that apply to the expenses you enter, and it tells you if you have enough to use your itemized deductions or if using the standard deduction is more advantageous for you.  Under the new tax laws, some deductions have been capped—there is a $10,000 limit to the itemized deductions for state, local, property and sales taxes. 

2022 STANDARD DEDUCTION AMOUNTS

SINGLE $12,950  (65 or older + $1750)

MARRIED FILING SEPARATELY $12,950  (65 or older + $1750)

MARRIED FILING JOINTLY $25,900  (65 or older + $1400 per spouse)

HEAD OF HOUSEHOLD  $19,400  (65 or older +$1750)

Legally Blind + $1750

There is not a first time home buyers credit on a Federal return. That ended in 2010. If your state has such as credit, you will be able to enter it when you prepare your state return.

Buying a home is not a guarantee of a big refund.  Your deductions for homeownership combined with your other deductions (if any) must exceed your standard deduction to change your tax due or refund. If you purchased your home late in the year, you do not even have a full year of home 

ownership deductions.

Your closing costs on your new home are not deductible except for prepaid interest, prepaid property tax or loan origination fees.  There are no deductions for appraisal, inspections, title searches, settlement fees. etc.

Your down payment is not deductible.

Your homeowners insurance for fire, hazard, flood, etc. is not deductible for your own home.

Home improvements, repairs, maintenance, etc. for your own home are not deductible.  

Homeowners Association  (HOA) fees for your own home are not deductible.