Single mothers

I’m about to be a single mother here soon. I have an 18 month old however I’m scared to leave him. Terrified that his dad will leave him to fend for himself or let him roam around not watching him. However I’m gaining a desire to leave his dad for good! Now when I have to share custody during the days I don’t have my child, how do I deal with being alone? I don’t want to be alone but I’ll have no choice and the whole time I’ll be worried about my child. It’s just hard to even consider. Idk how did you all move past that feeling of only having your child part time vs full time everyday being a stay at home mother for 18 months. Ugh.