It would be complicated, if you wanted to date you would have to be on someones friend list for three months and be in parties with them for a week at least four times a day and complete a at least 5 levels in each run you must gift each other once.
To marry in game you have to gift each other ten times be "in a relationship" for at least 9-12 month after you make it official that your dating.
When your married your share inventories. You can use but cannot sell each others items (excluding money and CE)
Divorce is simple you each leave with your half plus you split what you made together while in a relationship.
NOW BEAT MY IDEA INTO SMITHEREENS HAHAHAHAHA.....
Oh my sweet pepperbox... what in the name of Agni is this? marriage in spiralknights? good Vog no, PLEASE NO. Players are not ready for this kind of commitment to one another!!! O_O
However sharing inventories is an interesting concept but eh... it's just that... interesting.