Leslie, I worked at a winderness/residential program and there was a very similar situation with a mother and her son. He would take any crumbs he could get from his father, and his mother, who did everything, was there for him and supported him through everything was always treated as the "enemy." He blamed her for everything, even though the one time he lived with his dad, it lasted for two weeks before his dad sent him back to his mom. Much of the way he treated and viewed his mom was through his dad's lack of responsibility - never being the support, only being the fun dad who goes on short fishing trips, etc... doing the easy stuff. But the mom would continue to take him back, try to make things better, panic about his poor decisions, and be hurt by his criticsm of her. I can't imagine how difficult that is as a mom who has put everything into her son, but she also had to come to the realization that he was an adult and she was allowing him to treat her that way. She's very sweet and we're still in touch on occassion. I'm not sure how her son is doing right now, but she's taking care of herself and that's the first message i think that needs to be sent. he would play the game between her and her ex and make her feel bad about moving on because it created the triangle he needed to not grow up (his dad taking virtually no responsibility and his mom taking too much responsibility). The sooner he learns that that game doesn't work, the better. Again, i can't imagine how difficult it must be, but the best advice i can give is to show him that you're going to take care of yourself and not destroy your own social life and well being just for him to go on being a child. if he doesn't want to live in a dorm, be straight forward with him - instead of focusing on it being a poor decision, tell him that if he's going to make that decision, it will bge his responsibility to find a job, figure out what to do, and grow up... and that you're not going to be his backbone. That you support him and love him but you won't support him making poor decisions for himself... and show him that you're moving on. If he has something to say about your boyfriend who he hasn't met, tell him you're happy and that's the end of the story. if he persists just to get under your skin, tell him you're ending the conversation and hang up or walk away. i wouldn't let the conversation go beyond the first comment he makes, because 1, it does no good to engage him in the conversation, and 2, I want you to take care of your own feelings as well. i hope this helps.
It is typical that the focus is on the parent's well being and not the child's. But this advice is bullshit.
Of course the boy is going to react negatively to any man in his Mom's house. That is the normal reaction with divorced parents. Despite the divorce, they still see their Mom/Dad being replaced and don't like it. This is a fear reaction. He fears how this may affect his place in your heart. He may not even be aware of this reaction and consciously think he doesn't like the newcomer. Just reassure the boy that your new man will not affect or negate your relationship with him. Reassure him he is still very important to you and let it go at that. Don't respond to any negative remarks he makes about your new man. Don't fee into it.
Don't over react to the boy siding with his Dad about the ticket mix up. This sounds like a minor miscommunication turning into something bigger than it is. Greg sounds immature, but hey, being out of social circulation at wilderness / TBS is likely to leave one socially backward. Just request the facts and if he brings up his Dad, say Dad has nothing to do with this, you just want reconfirmation of some flight numbers.
Focus on the positive. The kid wants to go to college and move on with his life. Encourage that. Encourage him in a positive way even when it means sucking it in sometimes and he will return the favor. You get what you give in any relationship. If you criticize, you will receive criticism. If you attack him, he will become defensive. If you react (over react) to his attacks towards you, you will only encourage him. You are the parent and must remain composed and in charge no matter what. That is how you gain the boy's trust. If you love and encourage, you will receive the same in response. That's just human nature. It's funny how we can treat family with less respect than we would treat total strangers.
When he starts college, tell him you love him and are proud of him. Tell him you know he will do just fine. That will mean more to him than the stupid car his Dad bribed him with. Your presence and Dad's absence at his graduation will also speak volumes.
Do not disengage yourself from your son's life. That will get you nothing. You will just lose each other.
And one last thing. Even when your son is saying, "I hate you!" Know this is just immature anger. He doesn't hate you. Show me a teenager that doesn't give his parents a difficult time and I'll show you a teenager that is not the epitome of mental health. Think of this as a challenge, not a disaster.