Mouth Guard.

When you work with someone close, get prepared to grit your teeth and buy yourself a mouth guard, the special kind, so you don't bite your own tongue off in the process.

I speak from experience. The sweet thing you call darling suddenly transform into a cold professional b*tch, and the sensitive chap you lovingly address as honey has become an MCP neanderthal. It's not always like that, but majority of the time, working with someone close suddenly brings out the side that you don't usually get to see: the rough side - and then you realise, ah, it's hard working with those nearest and dearest to you.

That's why people caution against going into partnerships with friends, because it might just turn sour - very sour. Having said that though, that's also where the sourness gets neutralised and become the sweetest trust, ever. Just that you'd have to go through the first year's worth of multitude of issues. 1 year, at least, just to work out the majority of the kinks.

Meanwhile, buy that mouth guard and book those holidays in advance.