I'm so sorry. This has affected me more than anything else I've read on here. Reading about how fucking selfish he's been (and I know sadly he's not unusual in that)- it's made my blood actually boil for you.
I've not been in your shoes exactly, but similar in that I had an infuriatingly selfish, lying, self serving low life to contend with and frankly my child is better off without him.
I relate to the heartache, the despair. I feel desperately sad for you, and beyond angry on your behalf.
I can tell you though that THIS is the low point. It's all upwards from here. Yes, it's a slow drip drip of a struggle but one day in the not too distant future , I promise you you'll look back and recognize how strong and amazing you are and have been.you WILL be in a far better place. Take from this that you deserve and NEED time for yourself. It doesn't make you any less of an amazing mum- just a happier one. Your boy will thank you for it.
I know none of this is consolation right now. I know you cant even see right now, through eyes so swollen and sore with tears and exhaustion.
But from this lowest of lows, it WILL get better. You've no idea how much people on here see willing good things for you. Stay strong and keep taking small steps, one after another. 
Please never forget that the support on here is heartfelt and real. You're not alone.