Right, I don't mind it when it's been set up so that you deeply understand why the characters are acting the way they are.

Though I still don't prefer it as a plot beat in general. Like, get over your issues first and THEN get in the relationship :P (And I speak as someone who did basically have something like a third act breakup with my now-husband... but if I wanted real life immaturity I'd, idk, read my journal ;) )