I have never suggested you stop paying his tuition as long as he performs the task at hand (does well in school). THEY will pull the plug if he doesn't.
I do suggest you pull the plug on spending money he has not earned and on the manipulation to get more spending money out of you. No one should be rewarded for lies.. and the problem is that, by your own admission, you do not know what is true and what is not. This is typical in relationships with addicts. We enable them to use by providing out of love or guilt or other various reasons. They manipulate and we stay in denial and want to believe.. and Oh I would be Thousands of Dollars ahead of where I am today if I had not played into the manipulation, put my head in the sand pile of denial and my XABF might be clean if I had not enabled him.
And my x husband might be alive today if I had not enabled him and been in denial for YEARS about his alcoholism. My "love" was as poisonous to him as alcohol and Rx pills.
My parents had no money for me for college. They were too busy trying to keep the mortgage paid, go to work, and provide food to be giving me money for college. The deal was that I had to go to college. I had to go for 4 years. I had to pay for it myself.
I did all of those things and graduated with it all paid for and with money in the bank. Wasn't easy but I did it. I worked three jobs.. and owned my own exterior painting contracting business and I was tired and it was hard but I did it.
Then I went back later and took engineering and math and chemistry courses.. and aced them and paid for them while running a farm and working full time.
so, that is what I mean and I understand your dilemma and your pain.. I truly do. We want so badly to do the right thing so our addicts can do the right thing. We want them to succeed.
some do in spite of the drugs.. but then some alcoholics function too. Doesn't make them any less addicted or alcoholic.
I do wish you well in this. Others here offer wiser advice.