So I land at Frankfurt Airport and the immigration officer asks me what I am doing in Strasbourg. I tell him I am getting married and he stamps my passport with a type D. I’ve been googling it, and a type D appears to be a long stay visa. Is it really a long stay visa? Will I get in trouble if I don’t try to see when it expires? Honestly I am still getting married but is hard because my girl has just started her divorce from her ex.
I'm guessing the stamp you're talking about looks like this (image from Wikipedia):
This is NOT A VISA, and in particular not a type D visa. It's just an entry stamp that documents when you crossed through the Schengen external borders.
The D in the upper left corner simply encodes that the stamp is from a German border guard. D is the abbreviation for Germany (Deutschland in German) in one of the several systems of country abbreviations used in Europe.
An actual visa is not an ink stamp but a colorful security-printed sticker in your passport that you need to apply for in advance. If you don't have one and were let in anyway, it must be because your passport is from one of the countries whose citizens do not need visas for short visits to the Schengen area.
In that case you need to follow the standard rules for short visits: No more than 90 days in the Schengen area in any 180-day period.