@rosine NOPE...it's not a YOU problem and you don't need your EX's 'blessing' to meet someone new.
I'm 42 and have run in to the same problems as you describe. My boy is 3 1/2. His mom left me just after his first birthday because she wanted a new guy...that came to our son's birthday party. How nice... Then she was out of here and straight in to his house, but anyway.
It took me 11 months to find someone and she got pissed about it and went off the handle, meanwhile loving her new life with her new guy. That relationship only lasted 3 months.
Since then it's been constant rejection or just flat out being ignored. Out of the many women I've tried to communicate with, only a very few responded and most of those once they found out I'm a single dad, GONE. I'm always up front, I don't hide him. Like you, my child is priority. I take care of him a lot, he's with me a lot.
I've tried meeting someone online and in real life and always come up empty. Online is mostly just scammers, spammers, picture sellers, prostitutes, people wanting you to buy their only fans crap and the one here and there that seems to be real will only communicate a few short sentences and then ghosts. One accused me of being deceptive right out of the gate because I said I have a couple of places, one in one part of the state and one in another part. That's "deceptive". Well...I do, but I guess a man isn't allowed to own two places? She never spoke to me again. Some people, like her, are very judgemental and form conclusions with no information to base it on. You can speak absolute truth and be called out for it, then rejected. Welcome to dating! I'm sure they're doing that to you too.
In real life, they're just as bad it seems. I tried hard to get a relationship going with someone I've known for some 15 years. I've known her son since he was a baby and would take care of him as if he were mine own and she knows it, but nope, she won't do it because she's so hung up on an ex who treated her like trash and dumped her. Ok, whatever.
Another I started talking with, she's also a single parent. We have quite a lot in common. We talked a lot about things for a couple of weeks or so and then out of the blue she said, "I don't want to be with anybody". Ok, so what was the point of the last two weeks? Why did you ask questions that someone who was interested would ask?
Another agreed to go out for a meal with me. I've known her probably 20 years, but then she backed out citing that we don't have much in common. What's that got to do with let's just go somewhere and have a meal?
So NO..IT'S NOT A YOU THING!! I've seen other people running in to the same type of thing. The dating pool is rough. It seems that women, even single moms don't want or are scared of, (I dunno what) of being with someone who will treat them good, will support them, love them and take care of them and who wants a family life. They just don't want that life no matter what they say. They talk the talk, but won't walk the walk.
Another thing I see are women who claim that are so tired of guys that just want to get in to their pants or who just want naked pictures. Well, they don't want a guy who respects them either and who just wants to take them out on a date and see if something might spark.
However if you were a career criminal, drug addict, woman abuser who ignores his child(ren), they'd be head over heals for you. It's drama and then they can complain to their friends for some sympathy.
Finding a decent woman who has her head on straight these days is a rarity, that's for sure!
Keep on being a good dad! Being a dad is the most important thing in the world.