A child of an ex-friend was allowed to stay in our CT home. Child is now an adult and has been helping with expenses (ie-room & board with no lease), but is causing extreme anxiety in household. Do I need to evict through legal means?

Yes, you will have to do a formal eviction if this person won't leave your premises.

Yes, unless you want to give them a reason to sue you, you will have to give them notice to move. And then if they do not, follow up with court to evict.