Can she just eat small amount of love so she won't be starve?
Yes, she can. However, no matter how small she take, it would still hurt the subject. That's why she has been struggling between her desire and conscience for so long.
That's so cruel.
Although Discord is officially converted to the good side in S3E10, I don't think he would really be good. He, after all, is the master of chaos. Decieving, betraying, misleading...etc could be very common for him. I think he would either be some kind of unpredictable character that has both bright and dark sides or still a completely evil villain who could make chaos in disguise and fool the world.
Anyway, Good thing is Discord can now freely walk on Equestria so if we want him to appear in our story, we don't need to think of why he doesn't take over Equestria or cause some terrible catastrophe. So here he is, team up with Fluttershy and think of a way to reform other villain. With Discord's godly power, it should be easy to do the job. However, things doesn't turn out that well.