Don't be too down on yourself. You were honest with your father and he sounds like he over reacted. That doesn't sound like sneaking around so I'm not sure I understand why your therapist is angry with you. Seems a bit extreme of your father to tell you (a grown adult) to break it off with someone he knows nothing about.
I think it is great that you are six months sober. There are many people who are incapable of that level of conviction. Keep up the good work and hold your head high.