He should have already, and he must have, NO Contact with this other (young) girl. ZERO contact. He has NO reason to have anything to do with this young woman ANY MORE. Didn't the therapist say this??

You need to stand up for yourself.

He should have done, but he will do it TODAY - delete and block her, on all phones, all social media. No exceptions. No excuses. No "one more call to say goodbye", etc.

Put your foot down. He can't have his cake and eat it, too! Heck no. You're his wife. You stand up to him!

Please set your boundaries, listen to yourself, and what would you tell your BF if she had the same problem.
If he does not want to get help, he will not change, you CAN NOT change him.
If he is seeing this woman, there are others, and not respecting you or the marriage. is his problem.
If you allow this to be your way of life, then you are setting a standard.
its painful to listen to yourself and listen to the truth, but you must no matter what it is.
trust yourself and stay healthy

If he was lying to you before he got caught, do you think he is still capable of lying to you now or that he has magically changed? It is hard sometimes. We want things to be better. We tell ourselves we should forgive and forget but this often negates our boundary setting. We become the one doing the giving and the doing while the partner/spouse keeps on being their old self. If you guys are still intimate, consider stopping that so you have more clarity. Sex with someone we are divorcing or we are no longer living with clouds our minds and hearts. There is an old book that fits your situation, Love Must Be Tough. The difficult thing about your husband is he is/was interested in someone so much younger. This is a power imbalance, he has the power since he is older. It may make you feel less than, less pretty, less young, too fat, whatever. Until you know the truth, do not believe him. I wonder if you could talk to the girl and find out what they are doing, having sex, etc. I hope he is not a college professor or a manager where she is his employee.

Additionally, if he is a false type of person, his nice behavior now may be a smoke screen to get his possession back (you) especially since he is in contact and has not blocked this woman on his phone.

Why did he move out? I find it difficult to work on anything if the person isn’t there to work on it.
It also give him the ability to work both of you.

For anything to work, there needs to be NO CONTACT at all!! If he can't hit delete and have no contact at all with her... he is still holding onto her just in case you decide you want out! She is like his safety net... He should only be focused on you if he really wants to repair things.

Only you can answer that, but it might be a good idea to discuss that with the counselor and get his/her response and then try to work out with husband before doing anything life altering.