I believe that the Big 10 has had 11 teams for a while
Yes, the Big 10 has had 11 teams ever since Penn State joined, and it has been a mess for them. There have been lots of years (and this year is no exception) where they've had a shared conference title because everyone doesn't play everyone AND they have no conference championship game.
Notre Dame is in the conference for everything except football, right?
Nope. All of ND's other teams are in the Big East.
There is one team leaving after this season I think though.
No. The Big "10" is adding Nebraska next year to get to 12 teams. They will be splitting into divisions and adding a championship game next year.