I am both a Bangel and a Spuffy fan. Yeah that is right, I ship both 🙂
I ship Bangel while they are Bangel and Spuffy while they are Spuffy. Even in season 6.
Yes, it was an abusive relationship, but they BOTH abused each other, physically and mentally. Buffy exploited and used Spike, taking advantage of the fact she knew he was obsessed with her, and Spike exploited her and used her fear of being "different" against her once he figured it out to turn the tables and gain the upper hand.
I do think Spike loved her, and I think Buffy loved him, but not the same kind of love she had with Angel. A complicated love. With Angel, it was much more pure and true. A "true love" if you will.
With Spike, I think what they had was a mutual respect, and understanding of each other. They, in a way, made each other grow as people, for the better. So for that reason, I cherish the relationship. Yes, spike crossed the line with the attempted assault, but he did not have a soul, and so while not acceptable, it is believable that he would go there. But Spike, being a different sort of vamp in the idea that he has always held onto some human tendencies, became revolted by himself and thus went onward to get his soul. Most people do have to hit rock bottom at some point in their lives and soul search and go through various changes, and odd behaviors before they find balance and harmony within themselves, and that is what Buffy and Spike did for each other. If anything, I think Buffy's purpose in the Spike+Buffy arc was to teach Spike how to be a better man. I think she helped him more than he helped her.