I'm looking for stories with marriage as a strong part of the plot. I prefer stories with a male lead (no sexism, I just like to put myself in place of the mc and I can't do that with female leads) Stories with rape/infidelity/betrayal are also out of question. If the story has sexual content (mild or explicit) then even better.
Examples: 

-Arranged marriage: Marriage arranged by family members, without mc's consent and sometimes even without his knowledge
-Forced marriage: Different from arranged marriage in the sense that it's more sudden and one-sided. For example the mc is told, "due to the position you are in/ you just acquired, you have to marry this person", or an influential person orders the mc to marry her. 
-Abnormal marriage system: Like "Koi to Uso" where the government introduces you to a partner at the age of 16 and you are forced to marry her/him, or "Arcane Transmogrification" and its prequel book (both from this site) where marriage always occur between 3 women and 1 man. Another example would be "Loner Harem Meister" where a man can legally marry up to ten women, but the government punishes with taxes and other things those men who stay single.

The Demon and the Princess sounds like an exact fit for your request.