It's a hard call to confront or not. On one hand, you want him to know that cake eating is not an option. On the other hand, I would be careful about letting him know that you snooped. He can always hide it better then you won't be able to know anything at all.
If you ask him up front if he is seeing OW again, would he tell you the truth? That may be a better way rather than confronting him saying you saw the txt msg.
If you don't say anything, you can continue snooping and gather data, but you won't be able to really use it against him, just as information to know what your action will be.
Not sure if I would confront, but it is up to you.
