It's not clear what you're asking, but if you mean, "if I get married while in college, will my 529 distributions affect my girlfriend's FAFSA", the answer is no.
The 529 can only be used by you. It's not considered an asset of your parents or your girlfriend. From the FAFSA perspective, it's as though you had enough money in your checking account to pay for tuition and room and board.
If you mean, "if I get married while in college, will my 529 distributions affect my girlfriend's eligibility for financial aid", the answer is maybe. If your girlfriend is eligible for need-based financial aid, then her eligibility will be determined using a formula that takes into account your and her parents' assets, minus their Expected Family Contribution. If she is not eligible for need-based aid, then it won't matter.
If you mean, "if I get married while in college, will my 529 distributions affect my girlfriend's Expected Family Contribution", the answer is probably. The EFC is calculated based on your and your parents' assets. The 529 account is considered your asset, which means it will increase your EFC.
An increase in your EFC would probably decrease your girlfriend's EFC, because the EFCs of both students are calculated based on the total cost of attendance (which includes tuition, room and board, etc. for both of you). It's not clear how much of an effect the 529 distribution will have on your girlfriend's EFC, because it's not clear how much of the total cost of attendance will be covered by your 529 account.
