Infidelity Support Group
Any relationship in which one partner engages willfully in sexual relations with another outside of the partnership is considered to have experienced infidelity. This breach of trust is often traumatizing for the faithful partner as well as the relationship, and support is often needed to heal emotionally and to decide whether or not the relationship should continue after...
I would question your therapists intentions by asking you to leave her alone. In fact, I'd probably seek another therapist as he/she has given you poor advice. Many therapists are not well-versed when it comes to issues around infidelity, yours sounds like one of these.
If you want to start your rebuilding, she needs to be home with you. If she's still interested in going out and partying, then that's a totally different story. If she's the one who wanted the separation, then the feeling of drifting is real because she doesn't want to be with you.
Wishing you well.