I see timing issues here. You say that your girlfriend wants children within the next couple of years. To me that means that you would pretty much start trying to have children at whatever point you became a committed couple or got married or whatever you decided to do to cement your bond.

That is very different from planning to spend, say, 5 or so years together before having children.

Keep in mind that I don't know your ages, and I don't know what sort of career you have or what kind of time or travel demands it has.

Would some sort of couples counseling be possible for the two of you to help you to explore if your goals are compatible?