There are a few questions I have such as;
How old are you? How old is he?
Why are you "always" breaking up?
Maybe you're not really compatible. Life is too short to be trying to change water into wine or fit square pegs into round holes.
It sounds like there is a lot of immaturity going on.
Not many women would consider a guy with three babies with (three baby mommas) to be a "catch". You said: "..he told me all I can do is cry..." The reality is no one is "stuck" with anyone!
Everyone is entitled to have their own "deal breakers".
Anyone who hasn't figured out how to have sex without causing a pregnancy probably shouldn't be having sex out of wedlock.
These other children and women are going to be in his life forever and you plan to marry him that means they're going to be in your life too.
Sometimes the best thing you can do is imagine your best friend or sister were in your shoes asking (you) for advice. What would you tell her?
If you do decide to walk away make sure you legally file for child support. Don't set up any non legally binding "side deals".
Just because you're not together doesn't relieve him of his parental obligation. The child is entitled to financial support.