First off, well done. You've got through pregnancy, birth, the early day/weeks and these first 6 months yourself!! No small task.
I know you feel that things are bleak, but things will get easier. The anger you feel is justified and understandable. Your ex has done you guys a favour though: he's shown you who he is, and how unreliable he is (amongst other things!). You don't want that sort of crap around you/your little one. And believe me, if he could do it to you and your little one, then he'll treat others the same too. If OW knew about you when she got with him, then she's just as bad as him...and they deserve each other. He's no prize. So, it's probably better that he showed his true colours sooner than later.
My (first*) ex walked when I was pregnant with my eldest. We were together 3yrs, and about halfway through the pregnancy, he scarpered off with OW....and treated me/our baby like shit. They were dark days for me, but I got through it with kindness of friends and family (including ex's family who were disgusted with his behaviour). My DC1 and I made a fab life together. Ex tried crawling back after he split with OW (they had a kid together and he did the same to her when her baby was small), but I told him to sling his hook. Ex sorted his crap out, apologised to me/my family/his family for his behaviour and has worked hard to make amends, and he's become a good co-parent.
I found it hard being alone in the early days (difficult to see friends or even pop to shops in the evening if you've forgotten something!), and it would kill me seeing happy families all together when out and about. It was shit on postnatal ward when I was the only mum on my own (the other mums had their DP's/DH's with them but I wasn't allowed a nominated visitor to be with me - had to be the father). But friends would come by to catch up, or I'd just take DC with me to see friends (not to pubs or clubs as that wasn't my thing, but out and about with me). I did OU courses when I was Mat Leave and had DC1 on my lap whilst I was reading/studying, which was cool and gave me something to focus on. I didn't plan on being a single parent, but things did get easier. I learned to drive, I retrained and qualified as a nurse. All those successes were for me/my DC1, but also a big fat "f* you" to ex.
I met my now XH (*second ex - I sure know how to pick them!) when DC1 was little. We got married, had DC2 but he walked (long story, won't go into it here) when our youngest was 5, and buggered off with OW (and tried to crawl back some months later). I've learned that it is far better to be single and then you know what's what and who you can rely on for stuff...than to be with someone that is unreliable (the stress that comes with that nonsense is immense!). Your place is your own and you call the shots in that place. Your routine is to your liking and (within reason!) you do as you please. Sure it isn't easy, but it's quite empowering in a way. Give yourself time, be your own best friend, cheer yourself on....and remember even those in the most solid relationships have their owns sets of ups/downs.
My DC are older now, and I've been a single parent for longer than I've been parenting within a relationship...I'm happily single. :) Believe me, this is going to be HIS loss. Both my exes have regretted their behaviour and treatment towards me/DC. Both have openly said that to me and to their families/friends. You two will do just fine xx