Need some advice

hopefully a few people can let me know what they would do in my situation. I don't know what to do, I am developing feeling for a girl and want to tell her how I feel, however there are a few things that make it harder to know what to do. the first issue is that she has recently got back together with her ex boyfriend, the second issue is that her sister is one of my close friends and the final issue is that there is a 5 year age gap. if you could please let me know what you would do in this situation I would be grateful. thank you very much for your time.