Single mom guilt

I'm divorced from my first husband.. I have a 3 yr old son from that marriage. My new husband and i have a 9 month old and he has a 10 year old.. we all live together.My son didn't really have terrible twos.. But the threes have been unbearable. He's strong willed and assertive. Things need to be on his terms. I feel so much guilt for yelling when he misbehaves. I'm terrified that doing so will make him want to be with his father, who lets him do what he wants. There is manipulation coming from that side of the familyI feel like I lose my temper more than i should. I'm overwhelmed with 3 kids . My son is getting older and more independent and I miss him being a baby and me being the center of his worldI feel like a crappy mom. I feel bad for having another baby and not giving my son my undivided attention like I used to. I try to do fun things with him and make memories but if it doesn't go perfect or I get frustrated I feel like a failure as a parent.How do I over come this. via /r/Parenting http://ift.tt/2eR6Ozj