Loving God leads us to love others for His sake: everyone who belongs to Him; which is to say, everyone. Here's St. Thomas on friendship:
When a man has friendship for a certain person, for his sake he loves all belonging to him, be they children, servants, or connected with him in any way. Indeed, so much do we love our friends, that for their sake we love all who belong to them, even if they hurt or hate us; so that, in this way, the friendship of charity extends even to our enemies, whom we love out of charity in relation with God, to whom the friendship of charity is chiefly directed.Fr. Victor Brezik, CSB, in an article on Friendship with God, takes it a little further:
By this principle of loving not only a friend but also whatever pertains to him, we understand why charity obliges us to be disposed in our hearts to love all human beings, if not even other animate and inanimate beings comprising the environment, not that the latter can be loved as friends, since they lack rationality, but that as creatures they belong to God Whom we love as a friend....(Thanks to Fr. Brezik for permission to post his article.)
