bless your heart, hope! i am 32 years old, married four years and pregnant with #3 (all unplanned).
my husband has been verbally and sometimes minimally physically abusive since our honeymoon. we got counseling; i kept a bag packed, but never left for more than a few days because it was "getting better"----and it was, a little. but it was still out of control and unacceptable. his depression, anger, and anxiety got worse until finally i did leave for a month last winter. i was serious, preparing for life without him, and he knew it.
i laid down the law, and he honored all my requests: counseling, weekly accountability with someone in our church, medication, try to check yourself in (he was SO depressed), stop selling drugs, don't drink every day, don't go out every night, don't sleep in until 2 p.m. he still doesn't fully recognize----or even remember----how he was acting, but his behaviour towards me is very, very different. not perfect, but under control. for now.
everyone's situation is different. i stuck with my husband because he was WILLING to get help and change, even if he sincerely had no idea what he was doing wrong. also, he was a very loving, involved father.
you are wise to be scared, really; and this is such a rough time to deal with a crappy man. i'd say, decide what you want/ need, meet with a third party you trust if possible, and lay out what you need from your BF. he can take it or leave it, but at least give him the option to decide. and have a plan for whatever he does decide. written down, so it's harder to just get soft and let him come back without coming through.
best of luck, dear. hold on tight.