Telling a Woman in a Relationship I have feelings for her

For the past few months Ive developed feelings for a Woman who is the kindest most nurturing person I have ever met. I get the sense she like me too. Whenever we talk she giggles. I once told her how kind she is and she blushed a lot. Ive caught her giving glances my way. The thing is she has a boyfriend. From what I can tell he does not treat her the best, I think he is avoidant. He makes fun of her good traits like her kindness and quirkiness instead of appreciating them. Im not mr steal your girl but a person this kind is really special and rare. She is so gentle and nurturing, always thinking of others, always helping. Is it ethical to let her know that I have feelings for her? Nothing dramatic or over the top or making her feel pressured. I want to express that I like her and do not need her to respond and that she is amazing and no matter what I will continue to support her. What does everyone think? Thanks so much in advance for any advice you can offer.