Her lack of reciprocal feelings for him.
Lack of confidence.
I get what you’re suggesting: love always finds a way. I wish that were true, but it’s not. Love sometimes works out, absolutely. But it is just as often thwarted despite our best efforts. We live in an imperfect world, and we don’t always get what we want. Things don’t always work out like we want. Call me a cynic; I’ll tell you that I’m being realistic.
That’s why it is important to love someone fully when you do have the chance, to be bold and take risks and express your love while you can, because you never know when it might be taken from you. Life is short, and tomorrow is promised to none of us. Neither is love. When you see it, go after it, and when you have it, cherish it.
Thanks for the question.