Ran out of likes ,so meanwhile i will give a like in spirit 
Another point i would like to add is that the transition from hostility to love needs to go smoothly to be beleivable.
This can go in many ways,, but some common ground, even if is little, needs to be established.
Perhaps, both have a strong sense of honor or love the thrill of a good fight, making them enjoy their encounters more than what they would like to admit to themselves.
Maybe they befriended before realizing they were fighting for opposite sides, making their hostility almost in name only and their encounters oddly cordial.
It is possible that during their encounters they may try to persuade each other to join their side.
There can also be some circumstances that may make this respect and potential affection more visible, like both being forced to work together to survive or defeat a more dangerous threat.
If i had to summarize, i think is important for the characters to have a genuine chemistry, a common moral ground, even if they don't agree on everything and a smooth transition from hostility to affection.