Have you ever heard of the marriage penalty? It means you could be taxed more as a married couple than you would as single people making the same amount of money. This is because single filers almost always have higher income thresholds when moving to higher tax brackets. Personal exemptions and itemized deductions can also phase out more quickly for married couples than for single filers.
The marriage penalty might not be a reason to skip matrimony, but it could motivate you to find out more about how taxes may change for you and yours.