This will probably be an unpopular opinion, but maybe Papa Augustus walked out because he was sick of walking on egg shells all the time.
I don't think understanding why someone may've done something is the same as thinking it's even remotely justified.
I'm tired of plenty things in the relationships in my life (things about my marriage included), but even if I somehow reached my breaking point, the correct way to end a marriage is not to go "welp, I'm off to a tropical island". The contextual clues don't seem to point to an adult breakup and divorce. Framing it in terms "he was just sick of it" is... weird to me. It's generally accepted you don't nope out of something with no warning (which, again, contextually seems to be the case) just because you're sick of it. Even taking the moral dimension out of it (which we shouldn't), it's plain irresponsible.
Also, my brain is probably out of whack from browsing "egg" memes recently on the Internet (EDIT: transgender identity-related ones. Apparently it's not the first thing Google comes up with when looking up "egg meme". Sorry), but my brain can't help but be amused at the (accidental, I'm sure) double meaning I see in the phrase "egg shells", especially as you spelt it separately. Speaking of which, we never had an indication in the comic as to what age Claire came out as trans, did we?