Your GF needs all the support she can get right now, she has her plate full. It's her MOTHER for god sakes, what do you expect her to do?! Stop caring for her sick mother and baby sit you?! Worry about your feelings? How would you feel if your partner walked out on you when you were going through hard times? It's not always about YOU! You are being selfish.
Then again, you cheated on her numerous times maybe it's best if you just walked away. She doesn't need anymore drama.
Just my .02