Woah. Your site is really nice, great work. I'm afraid we're very unlikely to add character tags. As much as that might be a nice thing to have, the site isn't really built to support it.
Please no. The couples aren't that clear here and deciding on for example either one of "Piyo x Tsubaki" or "Piyo x Kaname" will give people the wrong idea of what's official.
The idea of pairing tags has been floated in shadowy backrooms before, and I (as one person, who doesn't have final say) am perfectly open to the idea. I'm not convinced we would need to pick one pairing tag per character, and that seems needlessly limiting given the series' variety. Ideally, the tags would follow exactly what content is depicted. So that should be a non-issue. However, I'm just a casual reader here, so I could be totally wrong on all of this.