To the best of my knowledge, there is no instance in the OT that teaches to love your enemies.You are right. The closest is Leviticus 19:17-18:
You shall not bear hatred for your brother in your heart. Though you may have to reprove your fellow man, do not incur sin because of him. Take no revenge and cherish no grudge against your fellow countrymen. You shall love your neighbor as yourself. I am the LORD.Jesus extended this precept beyond countrymen to enemies.
Yes, but "just" is ciritcal. Thank you for this excellent post. Another fine exmaple that the OT is not a full revelation, and that Christ brought it to its intended fullness.