A free mod for Fallout 4, by mooglechick fka friendlyyan.

The Player Marriage Mod is a simple and easy-to-use application that allows you to get married to any romanceable companion at the All Faiths Chapel in Diamond City. With your romanced companion following you, simply head to Diamond City to register on the terminal inside the Chapel and then attend your wedding!

In this mod, you will find a new option inside the wedding ceremony. Now you can get married to any of your companions, but not to non-romanceable companions like Nick Valentine, Deacon, etc. You will have to talk to your companions before the ceremony begins and give them some kind words. Afterward, you will be married and have a short time to enjoy your new status as a married couple.