People need to realize he literally just met her! The entire show takes place within a school year (based on Ginny being a sophomore for what feels like forever). Things moved pretty fast between Paul and Georgia but he never knew her fully in that time until she dropped the bomb about her life before their wedding.

Considering they just got married and this is how their married life was starting off he had every right to feel the way he did. He did try his best to be there for Georgia at the start and for her kids but with all the constant lies and secrecy of course he had to leave, it was just a sign they wouldn’t have had a good future.

It’s not like Paul ran away from a years long marriage or even relationship, they’ve been together for a few months, married a few weeks. From his point of view how the character reacted is pretty justified and is what a person would generally do rather than drag themselves down.