If she already knows how you feel about her and she still sticks
with her boyfriend, then you are a bird-brain to stick around the
two.
On the other hand, if you stick around with her hoping that the
boyfriend will be more of a bird-brain than you are and will make a
mistake, she might fall right into your lap. That's clever
thinking. I call that gambling.
But then if she continues to stick with her boyfriend even if he
has already done something wrong to her and she does not go over to
you, then she's the bird-brain. In which case you are better off
wasting your time looking for a better girl.
But if she does not know how you really feel about her then you
will indeed suffer in silence.
If I were you I'd tell her about my feelings and then I'd go away
and leave her and her boyfriend alone. If she has feelings for you
she will come after you and try to explain "something" or other to
you. If not, then you are better out of her face.
The ocean, as they say is full of other kinds of fish, right?