I don't see what the grounds for friendship would be. Ideally, the two of you should wish each other well and treat each other with courtesy. Hopefully, you can collaborate appropriately in your roles as co-parents. There might even be occasional favors you and he might do for each other. None of that rises to the level of friendship, necessarily. Friendship is a pretty sacred thing in my book. Formerly married people normally do continue to have concern for each other's welfare. In some cases there does emerge what could be described as friendship. Maybe someday the two of you will have that. But you don't right now, and I wouldn't try to force that.

What you've gone through has left you feeling betrayed. It's appropriate to feel that. Let's not try to dress this up as something that's fine and okay - like he needed to move on and you need to be fine with that. You don't. The ending of this marriage was not a mutual decision. You were commited. He reneged. I'm not saying that anyone should stay in a marriage who really wants out of it. I would not want a man to stay with me because he feels he has to. But someone who walks out on me is not "my friend." Doesn't mean that person becomes my enemy, but this is someone in whom my trust was misplaced - if marriage means anything - so I'm not going to keep making that same mistake.

So, yeah, let him mind his own business. You don't need "fixing" by the likes of him. Be businesslike in your interactions with him. He lost his claim to being involved in "shaping" you, when he walked. Don't share with him what belongs to you. Spend zero time letting him advise you on how you need to conduct yourself. Learn to briskly change the subject when he gets into what's not his business. Do this and your self-esteem will be the better for it.

We know that, in his eyes, you're not good enough. That's why he left. But "not good enough for him" doesn't need to be your assessment of yourself. Are his values so impecable that he should be the arbiter of your worth? Maybe they are. Maybe he has accurately appraised you, and you are so severely flawed that no one in their right mind would show you the time of day. Yeah, sure. That's not what I'ld bet my money on. If anything, you've probably - for a long time - given far too much weight to what he thinks. I wouldn't depend on this guy's judgement to pick out a ripe tomato for me.

Go to therapy, if it would help you feel supported. You probably do need to work on boundaries. If you have trouble maintaining appropriate boundaries between yourself and him, then it's likely that this is an issue with you in general. So that's a good thing to work on. Being open to advice is a good thing, but one can be too open. If you're getting more unsolicited advice than seems genuinely helpful, then make yourself a lot less available as an audience for that sermonizing, or however he (or anyone else) does it. Before trying to have some friendship with your ex, I think you first need to master backing him off. It's a learnable skill, no matter what type of personality you happen to be.

That "so many people" are "commenting" on what's not their business tells me that you are probably too open and approachable. You're being disrespected. Try taking a lot less interest in what people think. They'll notice that, and you'll get targeted less. Never underestimate the vastness of other people's stupidity. I wish you well in the freedom and joy of your new independence.