Giving and receiving valentines (or, in Charlie Brown's case, not receiving valentines) is an example of the consequences of conditional love: if (fill in the blank), then I will love you/give you a valentine/etc. We are not called to practice conditional love, however, but unconditional love - because that is how Christ loved us. We live out that unconditional love through the three pillars of Lent - praying, fasting, and almsgiving - doing it not for the sake of being seen, but in order to show unconditional love to others for their benefit.