You and your crush's gender preference play a big part in love. Remember that a kiss may lead to breaking the friendship between you and the person. When the confidence is above 80% and the kiss meter is full and your crush isn't angry, stand near your crush and then press "K" or "Z" to kiss them.
When being in love with someone, you'll get the chance to kiss them. You can also tell someone is in love and who they are in love with if hearts form around them, and they say something unique about their crush. When talking with or about someone, the character might start to like them, which is then shown as a heart above their name in the talking bar and as sparkles on the actual character.