Can my work fire me if I have a doctor's excuse?
I got 2different doctor's excuses for days that I missed. However, my employer does not accept them or even notify that I have them. I have to miss another day now due to my fiance being committed for bi-polar and I had to get her to the hospital then to the center for treatment.
Do you have a contract? If you do, then the terms of the contract, including those regarding termination, disability, illness, and leave, must be followed.
Without a contract, yes, your employer can most likely terminate you for missing days at work. Without a contract, you are an employee at will, and employees at will can be fired any time, for any reason. Also, companies are not obligated to give sick leave.
IF you were already married and IF the company was large enough to be covered by the Family and Medical Leave Act, you might be able to take a leave day (federally protected) to care for your fiance; however, she is not a family member for purposes of the act. There is no right to take time off for someone who is not immediate family related by blood or marriage.
If the company is large enough to be covered FMLA (I think it's at least 50 people), you may be able to take FMLA leave--which is unpaid--for own medical care, though you have tell the company ahead of time that's what you're doing; i.e. it's not really designed for spur-of-the-moment sick days, and I don't believe you could retroactively go back and use it to validate days you've already taken.
If you have a chronic condition, it MAY be the case that it would qualify as a disability, requiring your company to take reasonable steps to accomodate you (though you have to ask for those steps). If you have a chronic condition, you might consult with an employment attorney.