My opinion is that if he's 27, you guys have been together for four years, and he's saying he's not interested in marriage, then that means that he's not interested in marriage. I'd take what he's saying at face value and believe him. That's the way guys are. They usually say what they mean, we just take it and complicate it by trying to interpret it and figure out what they "mean" when in reality they usually mean what they said. He's told you he's not interested in marriage, or in living together. Therefore, he is not interested in marriage, or in living together, even if he is willing to relocate to be with you. I wouldn't count on it changing, either. It might, but then again it might not. You've been together for four years; that's a considerable length of time. If he still doesn't know at this point whether he wants to marry you he may not ever know. He's also not that young, at 27. If he were 22 or 23 I'd think it was different, and maybe he was just too young to be thinking marriage in a serious way, but at 27 he's really not too young to be thinking about it. You also say he earns decent money, so that's not an impediment.
It would help if you knew why he doesn't want to get married or live together. If he won't even talk about the subject with you, that's not good. I don't blame you for feeling insecure that he won't even give you his reasons for not wanting to get married. It sounds to me like this guy really doesn't want to get married anytime soon, and you need to decide if you're okay with that or not. Do you need to be married to be happy? Is marriage one of your goals? Could you be okay living with someone in a long-term relationship without being married, or not? I don't think there are right or wrong answers to these questions but you need to know what you're okay with and what you're not and what you want. If you do want to be married (and that's okay if you do!) then don't settle for a relationship where it's not going to happen. Basically, I think you need to be clear on what you want, then talk to your BF and see if that's something he can give you. If he can't, then it's time to move on. I wouldn't stay in this relationship just because you're afraid of dating, if this relationship isn't moving in the direction you want it to. Don't stay believing you'll change his mind. You may, but then again you may not. It's not a reflection on you or how desireable you are. Some men just don't want to get married, and if that's something we want, then we have to find a man who wants the same thing. It's sad, but it's a fact of life. If this came out as harsh--I'm sorry. I just don't think the chances of him changing his mind after four years and suddenly deciding he does want to get married after all are very good, and I'd hate for you to waste your time hoping for that if it's not gonna happen.