There's just so many good little moments, where to start😕
One moment, a bit of which was in that you tube video was the bit in hells bells where Spike says Buffy's glowing, and buffy says it's because her dress is radioactive. That for me was one of those bits that shows that their connection is much more than merely lust, that theirs also a real warmth and mutual understanding between them about the things that are important in life and the things that are not so important. It was also one of the first times Buffy accepted a compliment of that kind from Spike.
Other moments that stand out for me are when Spike comforts Buffy outside her house when she's had bad news about Joyce's condition at the end of fool for love, even though he'd originally gone over there to try and shoot her, as soon as he saw her, he couldn't help but sympathise with her, and in crush there are so many great little moments, spike opening a door for buffy, and buffy responding, "what are you doing, is this a date?", and how crushed spike is at buffys negative response to him saying "Do you want it to be?", I love that moment, even though it can be painful to watch, feeling for Spike, still it just captures at that time how in love with her he is, and how oblivious to it she is. Some of these little moments in the dynamic of their relationship are what make all the other things in their relationship possible, and what make it so entertaining and believable at the same time.