With all due respect, I disagree. It is the people she is a bit distant from that allows her to confess her problems in s6 - Spike, telling him she was in heaven, and to Tara that she's having sex with Spike. Tara likely suspects something prior (the Birthday party). They hover on the outskirts of the inner circle of the Scoobies, so that's why she feels she can confess to them.
She cried because the reality of the situation has finally hit her. She's talking to someone after bottling up everything for so long, and enduring all the abuse from Spike. I don't think after her resurrection she'd really cried.
As for them being closer than we realise - doubtful. Also, Tara - not that great of a friend. In s5 when they think Buffy is having sex with Spike, it's Xander and Willow who are more understanding and supportive, with Tara calling her "nuts". She also breaks her confidence by telling Willow that Buffy slept with Spike when Buffy specifically asked her not to.
I know people like to build up their friendship, but the evidence shows otherwise.
As for Cordy, I agree. I guess over time they might've been friendly towards one another but not formed an actual friendship. Wish they'd had a chance to see one another again after a few years though.