No, no, no, no OP your DH has crossed a line so far that you need to ask yourself why you think you need to recover and not discard?
Your DH was texting a 19 year old for that amount of time, that is him choosing to do this, every single day, for 3 weeks, that you know off, that is the first bit, but to do that to his friend, and you?
That takes a very kind of special type of person to do that, and he will do that again, and again to get that high of excitement, this is not a little side step, this is a personality trait.
You need to ask yourself why you allow him to manipulate you in this way.
Did he own up to you? or you found out?
Because there is a huge difference in what you have to work with here.