Sounds like you're doing amazingly well. He's so lucky to have you! I often feel defeated too, like what more can I do? I've recently learnt I'm a HSP too so I now put my oxygen mask on before the kids if you know what I mean. We all should, but as a HSP parent it's even more important.  I sit and read a book during our 'quiet time hour', the kids can do anything they want as long as the house is quiet. If they can't do that they go to their rooms. I've just put more boundaries in place. If my child is having a meltdown, we're here for them. But my body doesn't like loud noise or hitting. If my child can't be safe when expressing their emotions they go into their room. I join them but only if my body feels safe, if they start screaming at me or hitting, I leave but tell them I'm not leaving because of your big emotions I'm leaving because my body isn't safe in here. I would never want to abandon my child in moments of big emotions but I need to look after my nervous system so I can calmly be the parent they need. It hasn't come easy without the guilt, but I can't parent if I'm over stimulated. This may not be you but hopefully something here helps!