I think what Lymehouse posted bears repeating and I'm going to go slightly against the grain.
I don't think "I don't love you anymore" is an understandable reason.
A reason? Maybe. But understandable? No. It begs the question "WHY don't you love me anymore"?
Imagine a film critic doing the same:
"I give "Toy Story 4" 2 stars. Because I, although I once loved the Toy Story franchise, I don't love it anymore."
So I think if you actually want your H to understand you'll have to present whichever of the the two interpretations Lymehouse offered - because I think these more accurately nail things on the head.
Are you REALLY saying:
'I can't cope with this (His illness and a little baby.) I love him but I can't care for him - it's too much. I'm depressed and feel numb towards him'?
Or, are you saying:
'I don't love him anymore and I really don't want to be lumbered with him, I'm looking to find an excuse for a way out which doesn't make me look bad'?
"I just fell out of love" is an incredibly passive explanation. It treats feelings as if their random clouds that defy the laws of physics.
PING! OMG! I love you!
*PING! OMG! Now I don't!
Totally not my fault! They just vanished like a phone signal affected by... well, who knows? The weather? A technical error? It doesn't matter - all that matters is they're gone.
And that might be true, but again, that doesn't it understandable. Because if feelings can just switch off for no given reason they why can't they just switch back on again, for no given reason?
And truly, if you want him to have a hope in Hell of finding someone more suitable for him, then you definitely owe him more. Because if you don't, the most perfect person may come along but he'll be thinking "well, she might seem perfect but experience has shown me that any feelings she has could switch off randomly at any point and that will be perfectly valid - I'll be abandoned again and confused and I just have to accept that. In fact, given its already happened with a person I loved I should EXPECT that will happen.
Take it from a person who wrestles daily with this myself. I'm long over my divorce. We have a very amicable arrangement. I would love another relationship, but I just can't trust myself to start one because - if my take my ex at her word - no matter how suitable or infatuated the person is, they could turn on a dime and cheat on me just because "feelings change" overnight.