You sound pretty intuitive & with your head on straight so I imagine you do great with your kid & the situation. If it were me I would just keep things stable, whatever that is, with much order, keep letting the kid know what a great guy his dad is, as to his positive qualities, even if, "dad," isn't grown up yet & the kid may be way more mature than, "dad," will ever be, but always (as I'm sure you do) keep reminding him.. His dad needs to be his hero regardless, as you know.. then you come here & elsewhere & speak the nasty truth of the bad qualities of which the kids always know anyways.. but they SO need to hear the good about their dads..
Just keep raising the buffers around yourself.
Typically even when we want to be kind to their other woman/women whatever it is with them, during split etc.. they would block that too. BUT always helps to love & love some more.. you know all this, can tell your act is together on it. You can protect your son,that's good & motherly instinct, but just make sure his dad is his hero too, reality amidst, & as much order in your home as possible.
From your other posts here you sound very together, probably you are doing just fine, just don't doubt yourself.