OP, I can see how sensitive you feel about all this, so please don’t take what im saying as criticism or meanness. I know what it’s like not not be able to see the wood for the trees!
It sounds like your focus is on finding a man so that you have a family unit rather than being a single parent. That’s not going to benefit either you or your children. Already you’re putting up with being treated not very nicely...that’s not good for anyone!
You say you a terrified of being a single mum...I would be too! But it sounds like that’s what you need to focus on now. What can you do to be the best single parent you can be? Parenting courses? Therapy? I’m certainly not saying you are a bad mum, but you seem to be looking for a man to solve your problems when really you need to be looking at yourself.
Your children need the best mum they can have, not a random stepfather to come in and save the day. I think while you are looking for a person to solve your problems, then your decision making and man-picking skills are going to be dodgy.
You are enough for your kids. Putting up with unsuitable men just because they’ll fill the gap in your life can only end badly.
Parenting is hard, I know. Please focus on yourself for the time being and then when other relationships come along you’ll be in a healthier place with more self-respect, stronger and with good boundaries.