I think B00's right - you should stop feeling responsible for what he gets up to. Parents have it tough enough (as you know) but the way you said right in your first sentence that it seems somehow related to your divorce... well, maybe it is and maybe it isn't, but that doesn't mean you should have to feel it's your fault for something (perfectly reasonable) you did 14 years ago. You don't have to stop loving him - heaven forbid I should stop loving jno jnr even if he bcomes a psycho killer - but it's time to say, hey, he's 25, time for him to take responsibility for his own lilfe.
About needing his money: again, he's responsible for the rent he pays you, as he would be to any landlord. It's for HIM to sort out, not you. (I would agree that this advice isn't very helpful for you, though!)
As for what you're going to be asked - is it is lawyer who's summoned you to court? if so, ask him what he intends to ask, and what the prosecution might ask you. And tell the truth, don't be trying to make excuses for him (that's his lawyer's job). Whether he's guilty or not, it's up to him to answer the charges - not you.
I know, it's hard to tell a mother not to feel responsible for her child. But at some stage he's going to have to grow up, and you're going to have to let go. Maybe this will be the time he suddenly realises which way his life is going and starts thinking about what to do with it?