It's not my place to tell you whether to leave your partner or not - that's between you and her. Yes, things are said in anger. Many times, we say things we don't mean. I've been the recipient of many hurtful accusations from my DH before he straightened himself out. Your fiance may be hormonal, God knows I was when I had my children.
My problem was that I concentrated on the children and was accused of not giving my husband enough attention. That was before I began writing. Then I was accused of sleeping with every man I met. But that's another story.
After he went to the doctor and got his medication (yay!) he responded with mild enthusiasm when I told him I would like to write, and he helped me out by refurbishing an old Thinkpad for me to store my work (my handwriting sucks, and hurts, too).
After two years and two novels, and no agent or contract, his lukewarm support has cooled off somewhat. Still, he doesn't bother me when I sit on the couch, trying to edit my novel. He doesn't complain because he has no right. I dedicated countless hours catering to his well-being for twenty years, nurturing his neuroses and stroking his ego, and he can pay me back by not giving me any grief if I want to spend a couple of hours a day writing. God knows he ignores me for hours at a time, and it doesn't bother me.
He makes no secret of the fact that he believes my writing is only a hobby until I get my first cheque. He doesn't encourage me like other family members do, but so far he doesn't discourage me, either. I don't care. Whatever he says will not stop me from writing.
You guys may have to sit down and work out a schedule, or you can devote a set time every weekend for her, to do what she wants. Even if it means getting a babysitter so you can spend some time alone together, whether it be a walk in the park, a nice dinner, or curling up together to watch a slobbery chick flick. You gotta give a little to get a little. Just wait till your first sale - use the advance to buy your little baby something special!
If you find it difficult to respond to her heated words in person, use your writing skills and write her a nice letter, expressing your concerns in a loving way. But above all, don't give up your writing.