U+2764 · emoji since 2010
The red heart is the classic, no asterisks way to say love. Partners send it, parents send it, best friends send it, and it lands the same everywhere: I care about you, full stop.
It's also the workhorse of warm reactions. People tap it onto photos, good news, and kind messages when words feel like too much or not enough. Among all the colored hearts, red is the one that never needs explaining.