Can a person with celiac disease get married?

Q: I love a girl and I talked to her parents. Next year we will be married insha Allah! Problem is that I have celiac disease, and in celiac disease people develop many other complications and I am getting some. I am just 27 or 28 yrs old. Is it a sin if I marry that girl or should I remain unmarried? I'll leave pain and suffering in someones life. I am really sad. I think I have lost all the haqq to be with someone. 

Premarital relationship

Q: I like one girl and she also likes me but due to family situations we cannot marry now or do nikaah in public but to avoid gunnah of zina we want to do nikaah and when the time is right we will marry insha Allah. Is there any way in shariat that before we meet each other alone in any place before that, can we do nikaah by our own without qazi and witnesses? Can we do nikaah on our own?