The way I tag it, it's basically just the difference in the relationship lol. The thing that makes a yandere a yandere is that they have an obsession for someone that's so intense it basically makes them insane. Most yanderes are portrayed as romantic (the whole "I will kill to get with my crush" sort of thing), but that's not the only way to do it of course. It may just be because I don't get romance, but I like to think some of the best yanderes are the ones who don't try to label their love. It's just "pure adoration".
However, I make sure to tag stuff with "platonic" or "not platonic" cuz if you're like me, you might dislike reading stuff that has "exclusively romantic" things, like kissing on the lips, talk of boyfriends/girlfriends, marriage, etc. A lot of fics though don't have that stuff even if it's written with romantic relationship in mind. So I still tag somethings as platonic even if there are love bombs, cuddles and that sort of thing, cuz it can still be read as platonic love.