To add someone as a partner, you must first add each other as a friend and accept. Then while logged in grid go to Control panel here: http://tranquility-life.info/login.php?lp=/index.php and then when you log in on the left side click Manage Friends List. Look for your partner to be and click the green Propose Button. Tell them to accept. Once both have done so log off the Control Panel on website and also log out of the grid. Once you both get back in the Grid port to another region, say The Pier for example and the profile should now show you both as Partners. (Please don't ask why this is the case I have no idea lol)

***Please note, if things aren't so great and one person wants to leave the grid, then do your ex a favor and first you HAVE TO go to Control Panel again and Divorce them before requesting your account to be deleted. If you do not, they will never be able to partner another person as long as they have that account. They would have to create a totally new avi to add a new partner.***