The cultural differences between working where you are and for a western-style company can be significant, to be sure, and if you choose to pursue a job at a western company you're going to have to find some sort of compromise between the two.

I wouldn't worry too much about Famous Company not wanting you to talk to your current boss about it. Certainly you can't tell your current boss anything FC tells you that is confidential, but merely telling your current boss that you are talking to FC, and any non-confidential bits about the opportunity, is frankly none of their business. I can understand that FC doesn't want your current boss to be involved directly while you talk with FC (that's normal), but I doubt they care who you discuss your opportunities with (again, as long as you don't discuss any of FC's confidential information).

But I'm not sure any of that matters yet; from some of your replies in this post, I think it's pretty clear what you want to do. You want to be with your girlfriend, and that means staying where you are for at least the next year.

So, realistically, you couldn't accept an offer from Famous Company if they were to give you one in the next few weeks, and still do what seems to me is a higher priority to you.

I think it's fine to talk to Famous Company, but don't lead them on: be clear that you're not looking for new employment outside of your current city right now and that you may not be available for work until 2019. If they still want to talk to you, great. If not, I'm sure they'll be pleased that you were straight with them and didn't waste their time. A year from now, you might contact them and they may still be open to talking to you (they might even suggest this to you!). If your work impresses them now, I'm sure it will still impress them a year from now, and maybe more, as you gain more experience.

Regarding not burning bridges, that's a good instinct to have, and I think you have the right idea. Don't force yourself to act toward your existing connections in a way that makes you uncomfortable or makes you feel like it would make them uncomfortable, even if you think it's what a future company will expect. I'm not that much older than you (I'm 36), but I can attribute the majority of success in my life to the connections I've made and maintained over my professional career. Connections can always help lead you to new and better things. If a requirement for pursuing a new opportunity is that you have to treat your connections poorly, maybe it isn't such a great opportunity.

With that in mind, if you do decide you want to pursue something with FC now, absolutely feel free to talk to your current boss. From your description it does seem like he has your interests in mind, and you shouldn't keep things secret from him if you don't feel like that's the right thing to do. FC has no business in how you deal with your current employment; I don't see how they would get angry about you talking to your current boss about the opportunity with FC. You also have no obligation to tell FC that you've talked to your boss about it, at any rate. You shouldn't introduce your current boss to the people you talk to at FC, and your boss should not be involved with your discussions with FC. A western company would indeed find that very strange. But that doesn't keep you from talking to him about it privately.

Regardless of what you end up deciding, best of luck!