So there is a kiddo entering the picture. Brilliant.
Very sad for the youngster. And now you can see why it is never a good idea to bring kids into a picture that does not involve an established marriage that is steady, stable and built on love and trust. (you can also consider relinquishing the child for adoption and this way he will be in a home where he can be provided for by 2 very loving adults)
There is also a great deal of immaturity here --- how old is everyone? My guess is late teens.
Your FI isn't mature enough to be married and understand what commitment to only one woman means. I blame this on age, immaturity and hormones.
Your best bet (besides going back to school and learning good hard English grammar and syntax) is to scrap marrying this guy and make sure you get child support.
You will have your hands full with him and his undependability--- don't be surprised if he is barely around and does not spend any time with the child and don't be surprised if he's funky with paying child support. If he hasn't got a job, you know this is going to be a problem. And if he has a job, he will still be a problem to you.
And birth control. GET SOME and use it consistently. That's a good idea, too.