Well....how would you be taking care of the baby at 18 financially or is this bf going to have to take care of you and the baby by himself? Are you planning on working yourself? Babies take ALOT of MONEY and TIME and most 18 year olds aren't able to provide a baby with BOTH.
Then....you went and cheated on your boyfriend when you didn't get your way (he refused to try and get you pregnant). That's pretty immature. Sounds like you want what you want now and in a hurry. In this situation why hurry? Not to be rude, but you sound impatient and a bit spoiled.
He isn't telling you "no" just to make you miserable or suffer.....he is telling you "no" because he is using common sense about the matter which I will commend him for. I don't know his age, but he sounds reasonable and smart.
I would encourage you to finish school and establish your life BEFORE thinking about bringing a little one into the situation.
I can't imagine your mother is very happy about this pregnancy notion of yours.
You think your mother is "demanding".....well, have a baby @18 and you will realize the true meaning of "demanding."
Hi there and welcome. Your boyfriend is wise beyond his years. He is one hundred percent correct. YOU WAIT until you are established, financially secure, living independently from parents, able to take care of yourself before you have kids. You wait until you are in a committed relationship in which you don't handle things by retaliation--- cheating when you don't get your way is unacceptable. I will tell you quite honestly that it would be an awful decision for you to have a baby right now.
Get yourself into a stable position in which you can live on your own without your mom/dad/boyfriend or any other financial person to support you and then consider if it is time to have a child. But right now, you are not there. It would be beyond difficult for you to raise a baby in your current situation.
good luck