The Ex Factor

Organising a party can be a stressful affair, organising catering, venue, entertainments etc. coupled with the stress of formulating a strategy that will get all of your 'fashionably' late friends to the venue at roughly the same time is often more of a trial than we expect (I have cryptic little numbers marked in my address book next to certain names which allow me to keep tabs on roughly how late each friend is likely to be. Hence, if the party begins at 8 o'clock sharp, Rita gets told 7, Rick 7.30 and Pam, who is known for a certain excess enthusiasm, 8.15). Even with the best laid plans, you can still be reasonably sure that at any medium sized social event, a portion of your friends will show up late and drunk; another contingent will show up too early, proceed to empty the bar of house gin and be busy acting like foaming degenerates by the time your respectable aunt from Colchester arrives (on time) and still more will set out from their respective homes only to be distracted by shiny things, delayed by clueless minicab drivers, arrested, press-ganged into the navy or otherwise waylaid in fantastic and barely believable ways. Meanwhile the caterers 'forget' to provide a vegetarian option, the venue's lighting develops an unexpected fault leaving the party to continue by the light of candles and/or neon strip lights and the band shows up minutes before the venue closes with a two stringed guitar and a dented sousaphone.
You can probably tell by now that I've organised some 'interesting' parties in the past but, kidding aside, the aforementioned stresses pale into insignificance when compared to the tortuous process of drawing up the guest list. Now, this doesn't seem like it ought to be the most stressful aspect of a social event or even in the top five, but start to factor in past and present relationships between your friends and a can of worms (or more likely a bucket) starts to creak open. Of course, the easiest solution is to simply ignore all concerns of social politics and trust that your friends are mature enough to deal with things amongst themselves; if you do this, you're either extremely lucky or a fool!
Picture this scenario: Jim and Jane, both good friends of yours, were seeing each other for two years; they split up four months ago because Jim experienced some 'commitment issues' over moving in with Jane. Jim is now going out with Jenny, who happened to be looking for a flat when they got together about a month ago. Jenny moved in with Jim temporarily while she looked for a new place, and has been there ever since. Meanwhile Jane has started casually seeing John, another good friend who you've all known for years. Jane has 'issues' with Jim, and has quite publicly expressed her desire to scratch Jenny's eyes out with a rake. Jim resents the fact that his old friend John is dating his former lover and John is thoroughly bemused by the whole affair.
Now, I don't know about you but my head's spinning just looking at that last paragraph, and the last thing I feel like doing is worrying about whether to invite Jim and Jenny, Jane and John, Jenny and John or just invite all four in the vain hope that they'll somehow sort it in civil fashion amongst themselves (yeah, right!). And so, dear reader, I shall leave you to sort out this mess. Answers on a postcard please!