I grew up the youngest one of 5, my parents divorced when I was I think 8, and my father was really not part of our lives besides the occasional weekend visit which were really awkward moments more than anything else. I had to defend for myself since I was 15 really, that's when I moved back to the US from overseas and well, had no one (long story). I now understand the struggle, the pain, the frustrations, the fears, the choices my mother made raising us, why we couldn't afford new or name brand clothes, or even a finished house, she had to handle all of that by herself. You need to start by re-labeling your significant other from BF to what he really is now, your children's biological father. You are a loyal person, that is still hoping for the guy you fell in love with the first time you met him to find his way back. You can do that if you want, but I would rather ask you to focus on your life and your kids, and is gonna be lonely for a while, but ensure he is AT LEAST paying you what you need for child support. It doesn't mean he gets off easy, but I'll tell you how I honor my mother for all her sacrifice, I legally changed my last name to hers, because in my book she is the one that deserves a last name legacy. I don't know if this makes any sense but all I can say is that kids remember what their mother does for them. It was her teachings and her strength that kept me going forward when I had to face living in the US alone, at the age of 15. If it wasn't for all her advice, her teachings, her tenacity, her TRUE GRIT, then I would've never made it.
Ensure he takes care of his financial responsibilities first and foremost, and then allow yourself to discover yourself. You can still do it, but now you get to include your amazing discoveries with your children, and they will remember those moments the most. I know I do.

You got this, you're stronger than you've ever imagined. After the initial painful lessons, it becomes multitasking fun, and I think you'll love it.

Best wishes for you and your family.