The biggest question before revealing feelings about another person is asking yourself, “is this real?”
I had a roommate that would come home at least once a week and say, “I’m in love!” and be besotted with a girl he’d met. And he rarely had a second date because of his declarations of undying love, which could not in any way be true deep love because he didn’t know the girl.
Same with feelings of “I can’t stand her anymore”. While that may be real after one gets to know someone, one must ask oneself if it is a temporary feeling from frustration, or misunderstanding or if it is a real sign of incompatibility.
Once one has done some internal verification, then one can say what one feels. Just don’t expect it to be reciprocated.
And don’t keep saying it over and over.