2d8c9d896b532ec3 To get past the infinite connecting at the Main Menu, open Keychain Access, in Applications > Utilities, search for sims3 , and delete any entries you find.
For the fact that you can't login to the launcher, you could try deleting the file called [your email].bin in Documents > Electronic Arts > The Sims 3 > Downloads, if it's there. You could also try changing your password, deleting this file again (if it has regenerated), deleting the same Keychain Access data (if it has reappeared), and Safari's cache, all at the same time, to remove all data and start fresh. However, sometimes the launcher doesn't cooperate no matter what you do.
Is there a specific reason you need this login to work? It's not necessary for installing Store or custom content, and it has no real value at all aside from being able to purchase the advertised Store items, which you could do on the Store website instead. Plus, on Sequoia 15.5, clicking the Downloads button in the launcher crashes the launcher if there's anything to view at all, so you'd have no way of installing what you downloaded.