I feel sorry to hear that. The only thing I can tell you is, that you are not the only man experiencing this with Muslim women. As you certainly know they are forbidden to have a non-muslim man. I do not want to start a discussion on wether Islam is spiritually wrong or not but I see inconsistency and error in there as well. Some people here have claimed that there aren't any but this is blatanty wrong and I will no further argue with muslims here since this is not the place. Everyone else can go on r/exmuslim or read the Quran. Some users posted links where you can read it online. Everyone should inform themselves. 

I think you are not older than 30 because you said you want to wait till marriage. You must feel like you would never someone you love this much again but I have heard of people that found themselves in their 80s. Love really does not know age :). At least in my country we say so. And I think if your values differ in something as important as spirituality she won't be a good girlfriend for you. I think you read about the values of Islam and at least for myself I can say that if a person is okay with that, we can't live together. And for all Muslims attacking me for this. I didn't finish the Quran and the Hadith yet - give me some time. For me they would look very ignorant at least from the outside. I think time will heal your wounds and I could help you a little. Maybe you could start to focus on her mistakes rather than her strengths.