expression
with a view to marriage; with marriage in mind
Used to describe dating, cohabitation, or a relationship that is undertaken with the explicit intention of eventually marrying. Often appears in set phrases like 結婚を前提にお付き合いする.
彼とは結婚を前提にお付き合いしています。
I'm dating him with marriage in mind.
結婚を前提に同棲を始めた。
We started living together with a view to marriage.
A more compact noun form used in similar contexts, e.g. 結婚前提の交際, but 結婚を前提に is the full adverbial phrase.
A set phrase composed of 結婚 (marriage), を (object marker), 前提 (premise/condition), and に (adverbial particle), literally 'on the premise of marriage'.