It's the nature of kids not to appreciate things that are given to them. These things are seen as entitlements. They don't really start understanding the value of money, food, shelter, etc. until THEY are responsible for it.
As a father, I saw my purpose as putting myself out of a job. That is, to train my kids to be independent and self-suffcient, and also able to make sound decisions on their own. The fact is they aren't always going to have me. They have to be able to take care of themselves as adults.
By fostering dependency you are doing him a great disservice. I'd cut off the flow and tell him to spread his wings and fly. He may be angry with you in the short run, but after real life teaches him some lessons he'll appreciate it, if he has any sense. You've done more than your part. It's time for him to do his.
BTW, I would never tolerate my girlfriend dissing my Mother in our house (or elsewhere!). Jr may be 25, but still has to grow up.
Sorry if any of this sounds harsh, but you see where the nice guy stuff took the situation. You need to take control away from him and draw the line. I hope it works out.
Remember, it's not your job to be his buddy, it's your responsibility to prepare him for real life. Don't let yourself be manipulated by him ("If you cut me off I'll never talk to you again!"). Spoiled kids are good at that and some parents live in fear of their kids not liking them. I've had periods where my kids didn't "like" me. They got over it. I know they may not like what I say, but they know they can trust what I say.