I don’t believe the OT ever told anyone to hate their enemy. Do you have a passage in mind? Jesus doesn’t say it did in the passage you quote. He’s merely quoting a misunderstanding of the OT law before correcting it.
In fact, in Ex. 23.4-5, Moses said: If you meet your enemy’s ox or his donkey wandering away, you shall surely return it to him. If you see the donkey of one who hates you lying helpless under its load, you shall refrain from leaving it to him, you shall surely release it with him.
In Lev. 19.18, Moses said: You shall not take vengeance, nor bear any grudge against the sons of your people, but you shall love your neighbor as yourself; I am the Lord.
Jesus teaching what we call the golden rule was a quotation from Lev. 19.18, not superceding the OT.
This is in contrast to the command to love our enemies:
Psalm 139:
19 O that You would slay the wicked, O God;
Depart from me, therefore, men of bloodshed.
20 For they speak against You wickedly,
And Your enemies take Your name in vain.
21 Do I not hate those who hate You, O Lord?
And do I not loathe those who rise up against You?
22 I hate them with the utmost hatred;
They have become my enemies.