No one seems to mention the fact that if he had a t-shirt in his suitcase kind of suggests that clothes were being taken off.
Cheating is cheating whether they had sex or just kissed.
I don't know how long you have been together but i think once this has happened it changes your relationship forever.
I've had counselling, didn't do anything for me but were all different.
I think you would be better off without him, you don't want to spend all your life with someone you can never completely trust.
I hate it when the word "mistake" is used, a mistake is an accident & 2 people being intimate is not an accident.
If you truly believe you can forgive him that will give you a chance but as someone else said you will never forget.
I hope you make the right decision for YOURSELF.
I wish you well good luck.