Aries: Straight up drama queen. Will refuse to be around them and will make a scene about it if they have to. Has absolutely no shame. None at all. Shameless.
Taurus: Takes a long time to be completely comfortable around them. However, they put up with them, because they don't want to cause drama or be read as a non-chill person.
Gemini: Is friends with them but talks shit about them behind their back regardless. That's actually just a Gemini thing though, so we can't really judge them.
Cancer: Probably kind of wants to be friends, but won't pursue it at all because it upsets them too much. Wants to be nice, but hardly ever manages it.
Leo: If they're still angry at the person or were the one broken up with they'll shun them majorly and bitch too. Otherwise, they'll want to be best friends.
Virgo: Attempts to be civil, but it can upset them. Because they try so hard, they tend to regain friendship over time, but it can be really difficult for them emotionally.
Libra: Tries really damn hard to be nice to their ex. Doesn't always manage it - ends up talking about them behind their back but being lovely to their face.
Scorpio: Won't look at them, won't talk to them, won't be in the same room as them for very long. Gets annoyed if one of their friends brings them up.
Sagittarius: To be honest, they've probably forgotten that they ever gave that person the time of day. Sooner rather than later they'll treat them like everyone else.
Capricorn: Is 'polite' (read passive-aggressive) to their ex's face, doesn't talk about them behind their back. Probably takes ages and ages and ages to want to talk again.
Aquarius: Genuinely wants to be friends with their ex, which is a noble pursuit, but for obvious reasons it doesn't always go down as well as they'd like.
Pisces: Probably cries every time they see them. Once they get over them, though (usually not until they fall in love with someone else) they forget that they ever existed.