Thebg

My significant other will be traveling to the US in July under the Visa
Waiver Program to visit. Is it legal for us to get married during his visit
here? He has no intentions to live or work here and will be leaving the
country after a two week stay. I plan on relocating to his country
(Denmark) at a later time. Would this count as abuse of the VWP? Will this
prevent him from ever re-visiting the US?

CalgaryAMC

It is perfectly legal to get married on the VWP and then leave the country.

It should be noted that if it is known at POE that he will be marrying a USC, he will face very significant difficulty assuring the officer that he does not intend to stay. For that reason he should bring all the evidence he has available to demonstrate that he will be returning after the marriage, and that you intend to join him in Denmark.

He must not lie at the POE under any circumstances. That does not mean he should volunteer his life story, he should however answer any questions honestly and accurately, without unnecessary embellishment.

Chopper-Chris

You'll need to have evidence of the return ticket at POE, my advice would be to not even mention to the officer at POE that you intend to marry though...

it's just going to stir up the hornets nest and they may want to deny entry based on a concern that you will stay.