My theory:
May had been questioning her life choices for a while. Between the Elvis Marriage, being forced to make sandwiches for a crowd of incels at the Ralphamania (best Meight moment of 2023 until her escape in my humble opinion), the fact that Ralph 100% cheated on her with prostitutes right after the event, the insults to her family and financial problems caused by her husband's expenses and her daddy refusing to finance her degenerate lifestyle, the realization of how grim her situation was finally set in.
Add to that that Ralph has been spiraling heavily. I'm sure that off-camera he was constantly hollering, drinking and doing drugs and he probably smacked a bitch a couple of times.
At some point she must have had enough and told him that the marriage wasn't working and that she was gonna leave him if he didn't sober up.
Ralph in a rare moment of parial lucidity promised to turn his life around and offered to take her and he baby on a trip to Rome as his way to say sorry (and probably called her a nagging bitch the moment she was out of earshot).
Unfortunately when they were on the plane Ralph started hollering, probably because some random passenger had an image of a corncob on his shirt, until they were ejected from the plane and missed the flight to Italy, and that was the tipping point. I wish they had waited until they were mid-flight to boot them out but, alas, no such luck.