I feel so ashamed of myself for being so weak
None of this is anything he has done to you. He is now doing precisely nothing to you: he's not even there. What's happening now is that you're judging yourself negatively ('I'm weak') and then judging that view of yourself ('I'm ashamed of myself'), and this negative spiral can go on and on. Next you'll be disappointed with yourself for being ashamed of being weak, then you'll be angry at yourself for being disappointed with yourself for being ashamed of being weak, then...
See how it goes? Ditch the initial negative judgment. It's the thing that makes us crave the love of narcs in the first place. We class ourselves as 'x' negative thing, but narc tells us we're great, so that's ok. Even if they're sometimes not that nice to us, at least we get told we're great sometimes. And then even if they're mostly not that nice to us, at least we get told we're great occasionally. And then never, but at least they told us we were great within the last few weeks... and then few months... This is how they hook us in.
Ditch the negative self judgment: He hurt you very badly by treating you appallingly. Now, as any ordinary human would, you hurt. There's nothing to criticise here. It takes a long time to get over. It will take longer if you keep beating yourself up, and as soon as you stop beating yourself up, you'll be on the road to recovery. He isn't harming you now, you are.
His new woman is in for the same fate as you. Would you really want to go back and do it all again, knowing he's the kind of man who can do this?