Italian being the language of romance, of course it would have word-concepts to handle specific cases that can arise in this area. Thus, enter the saying la minestra riscaldata non è mai buona [it] apparently, from Venetian dialect, la menestra riscaldada no la é mai bona. A variant that made it all the way up to English speakers, though less known by true Italians, is cavoli riscaldati [it].
It means, a reheated soup is never good [en], that is, you should not try to revive past relationships. You can also use the short form minestra riscaldata [en] to refer to such revived relationships, or express it as a caveat [la] to a friend who would consider such a foolhardy venture.
Of course, for the same reasons, the Italians, God bless them, also gave us the beautiful trombamici [it] (trombamico [it], trombamica [it], trombamici [it], trombamiche [it]), which means, literally fuck friends [en], or, as I'd prefer in English, sex buddies [en].
If you ever go to Italy, you should be able to get along just fine by approaching women with a simple vorresti essere una delle mie trombamiche? [it], would you like to be one of my fuck friends? [en].
They even have the Ten Golden Rules of the Perfect Fuck Friend, and an explanatory table, included, I suppose, in every mid-school sex-ed textbook of Italy (click for hi-res version):
All you need to know is that farlo [it] means do it [en].
I should also mention that the Italian former Prime Minister, Il Cavaliere [it], one of the most powerful men urbis et orbis [la], actually considered renaming his political party to Forza Gnocca [it], which translates as Go Pussy [en].
Silvio il grande [it] (Silvio the Great [en]) is also known for having gotten himself into a scandal for having sex with a minor prostitute, which, quite fittingly, sports [en] the beautiful name of Ruby Rubacuori [it], Ruby the Heartstealer [en].
Of course, he got acquitted for that, yet didn't escape some community service time on "tax fraud" charges. According to leaked videos, though, he still managed to enjoy la dolce vita [it] (or is that il dolce far niente [it]?) even there.
As the French would say: ça ne s'invente pas [fr] – you can't make this shit up [en].