First, please forgive my poor English, cause I am an Asian.
Your response is so exact, that I couldn't help applauding. "Wife material perfect girl" is the most exact expression. But I think you are too meaning to others.
Sandra had done something inappropriate, I mean forcing change into Haley's bed when he is sick. I don't diss her overbearing, just mean her action is not enough respectful to Haley.
A perfect person doesn't mean every aspect of her is greatest, just like you couldn't let Sandra comparing treasure to Buffet. A perfect person doesn't mean he never does something inappropriate, everyone can do something wrong. A perfect person just means he has some great advantage that is just my care and has no significant disadvantage that is just not my care.
About sex thing, about bj for just meeting one or two weeks, I just tell a story. Have you played a PS Game "The Witcher"? The character "Geralt of Rivia", in our place, is called a walking dick by netizens because he makes love with every female protagonist. Some people said, "Geralt isn't a bad guy, and the bad guy is you! You made every choice! If you didn't do that, the thing will not happen."
The Same is true here. You make Sandra do that, the bad guy is the player! You can let them not happen.
About long distance relationship. In my place, some family commutes between two cities long time, or be on business frequently. They are just fighting for family. It is not a fault.
If Mc really love/like Sandra, he should struggle for solving the problem. For example, try to change a job in the city Sandra works in. If he can't solve the problem, the fault is from Mc, isn't from Sandra! Love is mutual, you can't expect Sandra dedicate for love alone. You have said, Sandra is his GF, not his mother. Even I suspect America's parents can do that for their children.
I said Sandra is perfect, not just because she is gentle, caring, and because of her striving for work and lover. Maybe the culture is different, I just say my viewpoint.
Don't mention the motive, the result matters! Some girl (now is woman) I acquaintanced, are from single parent family. They are very honey. I think it is a great character. People just love tenderly them, and don't take it for granted.
About OCD and mysophobia, I think it is a negligible thing because I think most people will accept it by getting along with her long, and can't fell uncomfortable.
When you are old enough, you will realize that you hardly meet a so good girl. You must learn to accept her some small flaw, that you can get together.
If the story isn't an incest story, it must be a very great book that can be published publicly. Good job, I love it!