He might well have felt that way . Don't we all at some time or other? When your spouse is dealing with terrible things you step up , you don't pout because your not getting attention and you don't say hurtful things to them.
It doesn't sound like he had a conversation with you about how he was feeling , and considering that fact , I think it's more likely it's a justification rather than a explanation.
You've had a miscarriage , a bereavement and your husband has treated
You terribly. You'd have got more kindness from strangers. Unfortunately some people react to this by becoming involved with someone else. Ask me how I know.
I'm sorry , but I would really consider a third party. It's got all the markers for it. Major life crisis , illness , a husband who has picked fault with you , but who has also done nothing to resolve it , and has now moved out and doesn't know if he wants to come back.
Nobody ever expects it and they'll deny it till they're blue in the face. People tend to work on a cost loss basis. You've seen it enough on here , people are unhappy but they won't leave because of upset kids and financial issues. The disadvantages of leaving often outweigh any positives so they stay put .
Your husband has risked his marriage , upset his son , left his home ect. That's a lot of loss and negatives for him. There's got to be , in his eyes at least , something positive in it for him to have gambled his marriage.
The fact he needs time to see if he wants to come back speaks volumes. He's not willing to end the marriage just yet and wants to keep his options open . Yet what's he doing about fixing the marriage? Nothing.
I suspect Op that if you do some basic detective work the reason for this will become obvious.