At the end of the meditation session dedicate all the merit or positive karma, the deeds of the meditation and prayers, to others—to your mother, to a neutral person, to a so-called foe, and to all beings as the cause of happiness, peace, and the realization of awareness of loving-kindness. Feel happiness for having this merit and giving it away to bring benefit to others.
If you dedicate the merit of loving-kindness to others or offer any positive deeds toward others with loving-kindness, you will generate merit, positive karma, and bring future happiness for yourself. If you give away your merit, it will not actually be lost or decrease—it will increase, because giving the gift of merit to others is itself an important and powerful means of merit-making.