In the dark

I have been with my partner for 3years.we have a 2year old.from day 1 there has been trust issues.hes never trusted me on facebook.so ive come off it. The main problem is he stays out. He says hes comin home but never does.ignores my texts and calls.and comes up with lame excuses as to what happend. I know i should leave him as hes clearly cheatin(even though he says he isnt). But what else can he be doing? Part of me thinks hes bak on drugs(cocaine). Im goin insane with all this.