For me, it's the pretty much every scene in Tough Love after Tara gets her brain sucked...
I think the bit where it really hit me was when Buffy hugged Willow and then hugged Tara, it just showed that, in a way, losing someone without them actually dying is even worse.
And the bit where Tara's sitting babbling happily to herself about 'they kill mice' and Willow's just crying silently...
and then when she says 'she's my everything'...
and another indirect one, when Spike says 'if it was someone I loved enough, I'd give my life for them' (I know I'm paraphrasing), that really got to me...
and the end, with the forehead-kiss and the 'I'll take care of her, even if she never... she's my girl'
Oh god, everything in that episode is so bittersweet, it's really tragic but their love for eachother is so beautiful, that gets me every time... and I hardly cry at anything!
