The biggest concern I have in reading your story is not the state of your marriage or whether or not your husband is cheating. It is the state of your focus on investigating and analyzing evidence. Why are you doing this? If all the evidence you collect convince you that everything is OK and he is not cheating, then what? You feel good and that everything in this relationship is fine and there is no cause for concern about him and the woman he works with? Will you have a loving, rewarding relationship with an engaged partner? Or would it just buy you some time until the next situation that leaves you wondering and that escalates into more doubt and anxiety that you have to alleviate by looking for evidence to convince you that what you gut is telling you is not true?
Your gut is telling you things are not right.
He may or may not be cheating, unless you catch him in the act, this pursuit of evidence is merely a form of distraction from the real issue.
You might be focusing on the investigations because acknowledging and facing the reality and considering next steps is too uncomfortable.
This amounts to spinning your tires in life instead of confronting reality and acting in your own best interest even if it is really uncomfortable to do that.
You either keep spinning your wheels and live in denial or
Tell your husband you are not happy in the marriage and seek marriage counseling or
Leave the marriage.
It may help you to get some counseling for your self if your husband is not interested in it, this will help you manage your anxiety, learn to trust your gut instincts, and help you define next steps.
Good luck to you!