Hard to keep going sometimes

I almost hate to say this but I have to.
The MOST diturbing part of the whole post was this part,

"My fiance doesn't really understand, she gets irritable and jealous if I am not working, even if I am so sick I can't get out of bed. I would like to get a degree in mechanical engineering, but I don't think I will have her support in it. Even today, she is upset that I am not working on the new house since I didn't go to work.

Just wish I knew what to do."

Ok, here I go.
Dump the inconsiderate *****, go on full disability and find something you can do on the side.
Not trying to be an *** or anything but she is just going to get worse, and more abusive as you get worse and less able.
Next you'll find out she is going out with someone else and talking **** about you while she's doing it.
Sorry, I know this isn't what you need to hear right now, but what makes you think she's going to be better with it later?
Selfish and inconsiderate of the situation now, worse later.
Just a fact.
Note what I underlined in what you said.
It's a BIG clue to what you have to look forward to with her.

Sorry