Then breakup with the girl. Since she can threaten to break up
over with you over such trivial matters, she can use the break up
threat on you again over other stuff. I can't imagine what your
life will be in the future if you settle down and marry. By then,
her breakup threats would have evolved to divource ones.
Try to rationalize and talk to her and get her to see the light. If
not, for God's sake, get out before it is too late.