Flying into Glasgow and going on to Denmark should not be a problem because you won't have to clear Immigration until you get to Denmark, I believe.
Can anyone verify for sure?
I would definitely NOT risk it.
The only way you won't clear UK immigration is if you have a scheduled connecting flight out of the UK with the same airline, as part of your ticket from the US, where your luggage is checked all the way through to Denmark. And even then, you would still need to apply for a Direct Airside Transit Visa (DATV) before you can fly through the UK.
If you have booked the two flights separately and will have to collect your luggage in the UK and re-check it onto the second flight to Denmark, you WILL clear UK immigration and will need to apply for a Visitor In Transit visa before getting on your flight in the US.
The LAST thing you should be doing right after a visa refusal is attempting to travel into or transit through the UK without a visa.
If you absolutely must see each other before trying to apply for the fiance visa again, then either he should travel to the US to visit you, or you can meet up in a third country, whereby you do not go anywhere near the UK in transit.
You got a good deal by purchasing the return ticket instead of a one-way back to the US, so if you don't use it on Tuesday, then it's not like you've wasted your money and you're not losing out on anything. Just think of it as making a saving on what would have been an expensive one-way flight back home to the US.