Crap, I was thinking of the S1 finale--the tornadoes, not the meteor shower, sorry. I was thinking of the earliest natural disaster that posed great mortal danger for both Bo and Lionel (post-Clex meeting) and I think that's the safest bet.

I'm more concerned about how gullible she's being, especially given the heinousness of his past crimes. I mean, he murdered his parents! Tortured her son! Fried his own son's brain! Changed or not, these seem like problem areas for a relationship.
I have a harder time with that too. Especially since one of Lionel's victims was her own son. Makes it particularly callous. The "dating widow" thing is only secondary and only because it's Lionel in particular.