Try to avoid is the best ... when a man goes out with a woman 1 on 1 even though they have known each other for a long time often causes misunderstandings ... unless they are siblings lol
i think the best would be if you can capture the pics yourself on your phone instead of hiring a P.I .. would be a waste of money imo ... follow her around if you need to ... when you have the pics show it to her & see how she reacts before you take the next step ...
If it has come to a point of no return i think it's best u start looking for a full time job, if not he has another excuse to use for divorce ... as some other members here said it is difficult if you do not have kids which i presume u do not have because of the problem you have ... hope it's...