Oh dear!
You sound very isolated and lonely.
Please don't be so hard on yourself, we all feel like shit sometimes, and yes even the best parents resents their child sometimes!
They are bloody hard work an even after you've poured in every I ice if your soul and being, they're still champing at the bit for more!
You are lucky to have three healthy dc, that doesn't mean your are going to feel it every second!
Does your youngest sleep ok? Could you get a sitter in while they are asleep? What about dad/ other family? Some kind of evening class would give you some me time and a chance to meet people. What about sign language, sewing, self defence or a knitting circle?
You need to get out and make so friends, you need some grown up conversation in real life!
If you really can't get out in the evening ( it happens, I bloody can't!)
How about some kind of activity with younger dc? Can you get him a nursery place for a couple of afternoons a week?
You sound like you feel very trapped and I need you to understand that's not because you are a shit mum who doesn't love her kids enough, it's because you are spending too much time with only them for company and that's not the way your brain is designed to work!
Sure start are a lifeline for me, I would be lost without them. Their services are for any one with preschool children so you can also try them.
There is so much help out there, please don't suffer in silence.