Thanks for writing in!
It seems you are really upset with this girl for not responding to your expression of how you felt towards her in the past. Is it really about her lack of response or is it her boyfriend's hostile response that you are upset about. What do you feel she is responsible for, how would you like to get back to her for it, how will this help you in the future? you need to ask yourself these questions.
On one hand, you do not want to hurt her, on the other hand, you just want her to know how you have suffered due to her and her boyfriend. What has stopped you from letting her know this for so many years? Now that she is getting married, entering a new phase of her life, what is it that is making you feel this urgency?
Will it help if you just write everything down, see how it feels for you after you have verbalized it, and then decide if you really want to communicate this with her. What would be the possible consequences if you choose to do so?
Sodhi, feel free to connect live to any of our experts here and discuss this further if required.