Why do you think Google has bad so much trouble delivering a product that is enjoyable to use in Google+? I understand the market saturation from Facebook, but something about Google+ is off. It should be a much better user experience.
I don't have the largest sample set to be candid. I should have specified that I am speaking specifically about relationships that end on good terms and both people make a sort of unspoken pledge to live their lives as if the other never existed. If the relationship ended in an ugly manner, all bets are off.
I'm going to digress a bit and talk about your friends specific example. First and foremost, if someone is sleeping with your girlfriend when they know you are dating, that person isn't a friend, let alone a close one.
In your example I would argue your friend clearly still cares about his ex if it hurts him to be around her. So maybe learning to forgive and having her back in his life as a friend wouldn't be the worst thing.
Obviously there are a million fish in the sea but there isn't a limit on friends. I personally had a bad breakup where I wrote the ex out of my life but I have now forgiven her and wish we could be friendly. But I certainly don't blame anyone for breaking off contact with an ex who cheated on them.
I'm not an expert but here's my humble opinion. Being an astronaught has very stringent physical and mental requirements. It's probably easier(or cheaper) to pick the smartest candidates from a group of very fit ones. To make a very crude analogy, it's easier to turn the star QB into a valedictorian than to turn the valedictorian into a QB.
I personally would prefer to be friends with exes. I don't understand why people find it so hard to go from dating to freidship. Of course it's awkward at first, just like your first date was awkward, but you push past it if its someone you'll enjoy in your life.
I've found with project managers more than other positions, you get what you pay for. The best project managers command exorbitant fees because of their reliability, to the point where bringing them in can be counter productive. But if you have the cash, you can definitely attract top level talent.