Easy, when you play with someone for a very long time you get to know each other better than in real life you would.
Connection such as this is more free and sometimes more intimate without any sexual relations, just mutual.
This sometimes leads to people making a sigh of their relationship by an in-game marriage, it's not the same symbolically but it does symbolize some sort of strong bond.
I'm usually soloing like Kirito does, so even against strong enemies (Powerful Elite's) i tend to go all out alone.
On my shaman in WoW I only died once when soloing higher level enemies, had bad luck encountering a spawned elite that was 2 levels higher than me

Back in the early years of WoW an elite mob was actually incredibly strong, even if you were around 2-3 levels above, it could still pound you quite easily, from what I know about WoW these days (i'm no linger a player) Elites only take 2 times more time to kill without being 8 times stronger than a normal mob.