Section 3 of the Act, which is codified at 1 U.S.C. § 7, simply defines the terms “marriage” and “spouse” for purposes of federal law. For example, federal law provides for benefits to a surviving spouse of a deceased military member. So you’re saying Congress has no authority under the Constitution to define the term “spouse” for that law?
Since the right to regulate marriage is not specifically delegated to the US Federal Government by the USC, yes, that is EXACTLY what I'm saying. The 10th Amendment could not be any clearer.
Just because Congress passes a law and asserts a right to define something, doesn't mean it's constitutional.