Hello my dear Marillion,
I understand. The first thing to do is to regain self-esteem.
To pity oneself, even unconsciously, is merely another way of delaying the work one will do on oneself.
First, I would like to convey the following message: a person can only be at peace with themselves and love themselves when they begin to accept their own weaknesses, to assimilate them, and to love them. No one is perfect, but isn’t that what makes the beauty of the human being?
When you see or feel that you are once again showing weakness in any relationship, learn to forgive yourself, which is in fact nothing but a lack of love that you fill by accepting that anyone who takes an interest in you enters your life. Perhaps, at first, whether in friendship or in love, you need to show a bit more reserve and keep a bit more distance. This is a way of showing the other person that your world, your life, is precious, and that you will open the door to those who deserve it. In short, people who will share your context while respecting your balance and that of your children, who need a mother who loves and is happy.
Example: As soon as you meet someone, don’t be available the moment that person wants to see you. Probe around, try to figure out who you’re dealing with by taking it slow. Don’t open up completely about your intimate life or what you consider your weaknesses. Show your strong side, the one that now, at 37, knows what it wants and what it no longer wants. This strength and composure will give you the support you need to start a relationship, whether it’s a friendship or a romantic one.
And then, what does it mean to POSITIVE? It’s simply moving from PASSIVITY, daydreaming, and the stance that leaves you as a victim, to ACTION. To positive is to act, to anticipate after having thought in a synthetic manner. In other words, instead of getting bogged down in a situation that will drag on for months in a way that makes you unhappy, you take the initiative and openly ask the other person the questions that are swirling around in your head. You need to look clear-headed, my Marillion, with the serene air of a woman in the prime of her life, at her most seductive, who knows what she wants, and who knows how to say NO, and GET OUT when it’s necessary. 
It is only by trying and acting that you will find greater serenity and a strong sense of self-confidence.
And since you have children, it seems to me that your relationship should be even more based on "if it's not this, then no!" (someone who is healthy for your children, who makes you feel happy whether you are together or apart, someone who respects you, is interested in your personality, seeks to get to know you, and lets you get to know them, someone who is mature in their head).
Stop suffering, my dear, try to act, to sort things out. Not finding the right shoe for a certain amount of time does not mean that you are the one who is flawed. It may be that you are not ready yet, that the time has not come. Perhaps you needed to ask yourself these questions to become aware of your worth. And to be aware of it, you need to define the things you enjoy doing even when you are alone: going to the movies with your children, taking a walk in nature with them, admiring a magnificent landscape, enjoying a good meal you prepared for yourself, with a good wine?, treating yourself to a small pleasure by buying a piece of clothing that will make you feel beautiful, changing your haircut or hair color?, taking a nice trip or a weekend somewhere? Listening to beautiful music, enjoying a great book on a subject that fascinates you, finding an activity that would make you come alive and that you could share with your little ones? It could be anything that would not come to my mind... Appreciate life for what it represents in your eyes and not through the gaze or the presence of another, of someone else. Your strength is Marillion.
Happiness is within you. Like the key, the answer. Everything is within you.
I hope I found the right words, as my intention is not to offend you, but for you to realize that you are the one who will decide your strength and your love for yourself. Everyone has this potential; all that remains is to discover it.
I wish you that strength. Remind yourself that there are people in similar situations who don’t even have the good fortune of having a child who makes you forget your pain when they smile at you or snuggle up to you… 
Good luck, and above all, don't hesitate to write whenever you feel like it.
It will always be a pleasure to exchange posts.
Friendship,
Natou