Depending on how she feels about you (which I assume could be the same since you said there have been feelings there before), you're confession could help her have the courage to deal with him better or break things off with him. Therefore, when she is not as the ultimate low point of stress and problems, and you do decide to say something, I would make sure you word yourself correctly and carefully. You cannot make it sound like an ultimatum. Don't say something like "I'm better then him, so dump the dude". It'll create pressure that doesn't need to be there. Instead offer her your love even if she decides to remain with him, despite how painful it may be for you. That way she'll understand that in the end it's really her happiness that matters to you and she'll feel a little more reassured your intentions are not completely selfish. The less pressure you set on her, the more I think she will come around to find appeal to you. And if it doesn't work in your favor in a reasonable amount of time, then leave it be before you get obsessed with something you can't have. That could work out too. Girls always want what they can't have, trust me ;)