Being "in love" is loving someone with passion. You choose their happiness over your own, you feel connected to them on all levels...sexually, spiritually, and emotionally. Please note this only works when both parties are "in love" with eachother. Otherwise you become very unhealthly.
you can love someone very much, Meaning you care for them but being in love with them, is that warm fuzzy feeling knowing that being around them makes you the happiest you have ever been. and knowing that things are wonderful.