It is important for you to know if your significant other is your tax partner so that you do not end up in an embarrassing position. Namely: let's say you thought that you and your spouse / girlfriend (husband / boyfriend) were fiscal partners (but in reality they are not), and decided to get a deduction for a non-working partner. Bottom line: you are denied.
– If you arrived together, being married, registered your marriage in the municipality (gemeente) and registered at the same address, then there will be no problems. You are fiscal partners!