To be fair, a good Thai Green Curry isn't difficult, so his ex wasn't Delia or anything...
Just think "She's a biatch, she had sex with my bloke at some point, I dont' like her but fair play the bitch could cook" then at least in your mind you are TRYING to be reasonable.
You're actually sounding like a human being so don't worry, if I'm honest I probably would never eat Thai Green Fucking Twatting Curry ever again, and probably never go to Thailand, just well, because.... however, that WBVU. And you did ask 
If I were you, put a 'comedy' spin on it that will make you giggle, first thing that popped into my head was the (the feminist within cringes) The Mad Lads.... She could cook, she could fuck, she could do the washing up, but insert DP's name had enough, she's gone, fucked off, shut up... never of course relay this to anyone if you wish them to think you're sane, but giggle inwardly... outwardly you'll be THE most reasonable person to have ever walked the earth. x