There must be something that u r not giving to him & he is finding it outside, Men don't like to complain & nag, instead they will look 4 solutions, but seems ur guy didn't find the correct one, instead, he went for the wrong solution.

Best thing to do is for both of you to have faith in ur relationship & start correcting things between u.

Try to know what is he not finding in u & work on it, make a change & make him feel it, spend more time with him, remember: he is ur first child!

Best of Luck!