What Rye said. The intent of the art is that their dynamic and body language when kissing changes over 3 months, likely the first 3 months of dating. In the first month they're probably going to kiss in a moment, it's still a bit awkward for them so there's a moment of hesitation before the kiss. Second month they're more relaxed and kissing while still being a bit reserved. The third month they're really into and are now passionately kissing with fiery intensity.