Hi, welcome
Ok, so if we consider the two extremes. One is that he was purely helping a lady that was trying to sort out her life. The other extreme was that he had a romantic attraction/feelings.
The first one is acceptable until you show concern and maybe a little suspicion. When that happens he should have respected your feelings and discontinued staying back. The second extreme is very much a possibility and is unacceptable but unless there is proof you'd need to stick with the earlier intent.
What is lacking here is respect for you with him continuing his routine. The residual anger you have might require couples counselling in order to ensure he doesnt take that avenue again and secondly that he realises the gravity of his actions.
Trust is so important in any relationship. When that trust is breached it becomes serious because it is very hard to get it back. I do think however that you have some good chance your anger will subside because he has told you everything, all the details it seems even his bosses comments, so he may have been naïve and kind. Even so you need a process whereby you can throw all those rocks in the river to restore your faith and counsellors are experts in that field.
I hope you are ok
TonyWK
