I am so sorry to hear of this pain for you and to hear about his behavior. you have been hurt in the past and to go through this again can be so painful. I understand how caught you are..tell him you looked at his phone or not. There is no perfect answer here...if you tell him the issue of his behavior will be lost and the focus will be on you and what you have done....terrible spot for you. But if you don't say anything then you are left with this continued betrayal and feelings of low self worth. I don't believe the behavior will go away...why would it? He will continue. If it were me, I would let him know what I know and go from there even while knowing the relationship may be over. But, isn't it really over if he is behaving like this? His choices have nothing to do with you and all to do with his disrespect.
I truly hope you don't take any of this on as your fault or you are not good enough. His choices have been hurtful and may be doing it to deal with his erectile dysfunction and feel less embarrassed even though you have been incredibly caring and kind around it all.
Such a tough spot for you and I just don't know that you would be able to sweep it under the rug and pretend it isn't happening. You run the risk in both ways for the relationship not to be a healthy and good one for you. So act according to what is going to work best for you and make you feel the best.
It is terrifying! I know that and I support either choice you make. I just want you to make the one that works for you...not him, not me or any of your friends.