I agree. This isn't the baby's fault and I really think your mom won't turn you away. There's nothing wrong about going to her for help. It's actually more mature for a person to seek out help when it is necessary rather than trying to handle everything yourself.
At this point, think about your children. Their father should start shaping up and being a real dad. He can't blame you for getting pregnant. It's not like you produced sperm and inserted it yourself. He should shape up and be responsible for the sex that he;s been enjoying.
Don't worry if you lose him. Your children deserve a father, true, but what they don't need is a sperm donor. Think about what you're worth and what your children are worth. Let him earn being with you and your children.
Your mom? Honestly, she's frustrated and she'll even be more frustrated this time. Can't really blame her. Think about how you'd react if you were in her shoes. After her initial frustration though, she will remember how much she loves you and your children.
Stand your ground and show her that you're an adult to be reckoned with. If you have to stop school right now just to concentrate on your babies, let it be. You're so young that once your youngest is five years old or even four years old and can be left at home with their grandmother, you'll only be around 25. Still so much left in your life and so many opportunities still before you. Think about how good it will be to come home from school with three adorable children to welcome you home. If the sight of that can't get you inspired to be the best woman you can be, I don't know what will.
Lastly, try to see things like your mom does. Look, she's hung on to you even with the frustration she has and the fear for your future. That's love, nothing else. It would be good to stick around with her. You can learn a lot about being a patient and loving mom.
Take care, sweetie.
We'll be praying for you.
Erick