In my opinion there are a couple of things going on here: one is that you don't trust your husband, and frankly if he's just gotten out of his first rehab stint I can only imagine that he's given you plenty of reason not to trust him in the past. Trust is something that must be earned. While I don't believe you have any right to the contents of his phone, he certainly does not seem to be behaving as someone who wishes to earn your trust, or who, at this point, deserves it.
The other thing is that you are obsessively attempting to control his behavior in an effort to make yourself comfortable, to validate things your instinct is telling you but which you don't want to believe. That is your codependence and as soothing as you imagine it will be to have answers, until you learn to validate and trust yourself, there will not be enough answers in the world to give you peace.
One option you don't list for yourself is "don't feed into the insanity and just take care of myself until more is revealed." I certainly wouldn't blindly put trust into someone who hasn't earned it, but I would very carefully pay attention to whether or not his actions match the words he is telling you about you being the only one for him, that he loves you and only wants to be with you.