See, I just don't see it as anything more than the bond between two warriors. Like Buffy had with Kendra. Faith is a whole different story, lol.
Yes, Buffy was honest about what she did or didn't want, but to me, the whole concept of them sleeping together felt really pushed and forced - not natural like Willow and Tara.
Willow and Tara's relationship built up over time. They started as friends, became closer until they realized there was something more between them. Which is why I don't think it was experimenting on Willow's part. If it was, she would have jumped right into bed with Tara. That, and after Tara, Willow considered herself to be gay. If it was experimenting, she would at least refer to herself as bi.
Buffy and Satsu's relationship started out as teacher and student, leader and follower, which to me is just unhealthy and sort of sets Satsu up for a world of hurt. Even if Buffy was honest about her feelings from the start, Satsu was still affected enough that she chose to stay behind in Japan to put some distance between them in order for her to get over Buffy. Whereas Buffy wasn't affected at all and simply reverted back to thinking of Satsu as nothing more than a friend/ally.