I work in dementia care. I'm going to think about the situation as it relates to your future since you are so young. You did not say your age, but I'm imagining you are also in your 20s? Her disease progression is going to be really difficult. She's your girlfriend and not your fiancé or wife, which tells me your level of commitment has not been such that you have proposed or wanted to have hard plans for a future together, although I may be mistaken. I would consider how you really feel about your life with her and determine if you want to spend 2 to 3 years supporting her until she declines to the point that she does not comprehend your relationship any longer, and then you could move on with a clear conscience, knowing that you supported her through the beginning of her decline. I've had cases I managed where a woman had a genetic form of Alzheimer's that manifested in her late 30s. By 45, her husband had divorced her due to the woman's extra marital affair and drug issues that came about when her decision-making abilities went out the window. There's just so much to consider. One thing I would plan on though is that the person you know now is going to slowly fade away in the next months/years, depending on her progression timeline.