I too feel that I am becoming a mistress to his own career. I guess I want to know if I do decided to start my future with him, should I expect to be constantly cheated on and be okay with it. All this said, God is love and fully understands and appreciates your problem. And that fairly constant theme has some deep implications your girlfriend will have to face. Mark an envelope to be opened at different times throughout the day. You may look on here and see all of us, but a lot of us got out much much older. He could never tolerate my work schedule, so I became a stay at home mom. It's not fair to put words in her mouth and thoughts in her brain like this.
While it's true that Mormons are not one-dimensional and completely predictable, the odds of a successful relationship, given the OP's description of his girlfriend, are slim. See, I am a SAHM and my husband has just gotten accepted into a 4 year pediatrics residency program this year. No doubt that some will be valiant up on the other side of the veil, but just as sure there will others who will reject salvation because of their high mindedness.
Lonliness is hard no matter the reason for it. There is no freedom to think, no freedom to speak your mind, and no freedom to do anything that 'the brethren' say not to. Does that make sense. Breaking up with someone solely because of religion is something people condemn alot on this sub when its a Mormon breaking it off with a non Mormon, but if floats both ways. Make sure she knows the plan, so you both can dress appropriately.
It's definitely not an easy life. Let's talk about kids. You should be fine as long as you stick to the lines you have laid out.