marriage of convenience 
noun
A marriage that is arranged for practical, financial, or political reasons: it was a marriage of convenience, to get the woman into England...
- So, ironically, real weddings used to be for arranged marriages - marriages of convenience.
- Well, some of these will be temporary marriages that are really marriages of convenience, that probably won't last.
- In this regard, the couple was not alone - plenty of their peers had undertaken marriages of convenience only to find emotional or physical satisfaction elsewhere.