I don't have ex, but my C6 has. I went into a boutique and he waited outside. When I came out, I couldn't find him as he stood far far away (about 10 shops away). I asked him why he stood so far away, he said he saw his ex in the same shop as I was.
He shd have introduced his ex to me! As I really want to know how she looks like, also I think my C6 should show off how pretty his wife is, haha!
My hubby is sensitive, so I would say 'old friend', 'long time no see', 'don't really get on but have to be polite'. These can all apply on an ex, so not really a lie.