Is physical intimacy during detachment period a deal breaker and absolute no or it is acceptable, maybe helpful?
Well that depends. Are you referring to intimacy with your H? then in that case, yes i would think OK. If you are referring to intimacy with a OP, well, then you must be prepared for the marriage to end... because it might. It might help you heal and forget, in some cases might even make H want to get back out of jealousy. But, if in your heart you want to reconcile, i wouldn't muddy the waters with that.
If you are referring to H having that with OP, then that is all dependent of you. Can you forgive and forget? If you are here, I am assuming that that is so.