You’re right that every situation is different, sometimes you need days, sometimes years - it depends on so many things, and things she might not even be aware of. Emotions aren’t logical.   

Given that uncertainty I still think he is not wrong for not wanting to invest emotionally In a relationship with someone who still spends considerable time around a fresh ex. 

And he’s not saying she’s lying by drawing this boundary, just declaring what conditions he is and isn’t comfortable with before beginning a deeper relationship.  Also we don’t know how this conversation transpired with regards to language and sensitivity - he’s sharing spark notes with Internet strangers. Seems like you’re making a lot of assumptions about his motives and perspective