The best way to make sure it doesn't happen again is to stay clear of him.

I would not want to go to him or anyone in his group because I wouldn't be able to have the level of trust needed for therapy.

Take care of you by not putting yourself back into that environment. Accept his apology if you want, then take charge of you and your therapy by finding another therapist who can help you with what you experienced with this therapist. I don't think another member of the group could do that for you and I wonder how you would feel about going to the same office and possibly seeing him as you work through what happened to you. He is not the person to fix the damage, he is the person who caused the damage and you need someone not involved in any way to talk to about it so you can talk freely and heal.

I agree with alex that while his apology is .. nice.. he is most likely really concerned with his own agenda.

Apologies are nice.. and sometimes they are another way of manipulating.