keep hope
I am wondering, as you've used those words, whether this is touching a nerve for you, that you don't already know, but instead hoping?
Why would you think that him dumping you is in any way related to you being unlovable?
People dump others every minute of every day, its not because they're unlovable people!
It's about the right fit that love flourishes. There's no harm in some self-reflection, so long as it's balanced with objective critique of him also.
I would be wondering why I didn't know things were wrong, why he didn't ever speak about issues that it came as such a shock to you, as it evidently has.
I am assuming he never moaned about stuff, about life, about how you did things together, sex life, etc? He has rushed into marriage/baby.
Maybe he secretly harboured resentment that your DC weren't his bio dc? Nothing you could do about that, but you could guess and guess till the cows come home. Whats cruel is that he's not spoken to you about whats been going on for him, and that's not a relationship anyway, thats just two people sharing the same space.
I wouldnt worry, you have no idea how this marriage/baby thing will end for him. It might look all shiney from the outside.
Also, all these men that fade away when it gets serious, were you in love with all of them? Are you accepting them all as compatible and serious and in love with when they don't feel like its a good fit for them?
You've been through two big breakups, take some time to lick your wounds and look after yourself, choose wisely and watch carefully with your next choice. 
You