Louise
You really do not want to face this from your H so you bury your head in the sand. It will only cost you further in the long run.
re your comments in quote marks.
"As for being weak, I have never being described in that way and I have never thought of myself as weak".
HE thinks of you as being weak, he knows you are not going to leave because you will and already have put up with this from him. He is showing you no respect whatsoever and a respectful man anyway would respect the mother of his children. He cares not for them either
"As I said no situation is black or white".
How black and white is this already; I doubt very much if he would be this forgiving at all if he found you made such purchases for a male business partner. Are you really then going to stay with him for the next 4 years?. You have really hung yourself by your own petard if that is the case.
"There have been a myriad of things that I've had to contend with that has made it the wrong time to leave. I suppose I just needed a listening ear because I really can't upset the children, now. They will cope better when they are older".
There is never a good time to leave and your son has already begged you not to divorce dad. He certainly knows something is amiss here and he is but a child. He cannot and must not make the decisions in your relationship with your H here.
You would like to think so re them coping better when they are older but they won't. Pulling the rug out from underneath them when they are venturing out into uni and the wider world will further destabalise their world. Rip the plaster off now and expose him for whom he really is.
You've already found cinema tickets, clothing receipts and a purchase for a sound system for her. What else will you come across now?.