If we are to love our enemy as we love our neighbor, then it is our duty to rebuke our enemy and not allow them to continue living in sin.
Leviticus 19:17-18
17 Thou shalt not hate thy brother in thine heart: thou shalt in any wise rebuke thy neighbour, and not suffer sin upon him.
18 Thou shalt not avenge, nor bear any grudge against the children of thy people, but thou shalt love thy neighbour as thyself: I am the Lord.
Your enemy should be loved by you, fellow Israelite, countryman, or otherwise.