What is this heart icon app?

Is your fiancee into K-Pop?

The fact that you trimmed the screenshot down to just the one icon made a reverse image search possible. And that symbol appeared in a few YouTube and Twitter posts about "K-Pop idol ranks", which led me to this app: https://play.google.com/store/apps/details?id=net.ib.mn.

Normally we aren't able to answer these questions: there are literally millions of apps, and the heart is a very common symbol used in many different types of app, and so unless it's a particularly well-known app it's rare that anyone can actually identify it. But this is more distinctive than the typical heart icon, a good visual match to that app's icon, and the image search didn't find anything else, so I'm hopeful that this is the answer.