All you can do is pick up the pieces and move on. I just broke up with my gf (2years) and less than 5 days later she fucked some other guy (claiming it was so she could forget about me texting this one girl...) so guess what, she obviously doesnt care, so why should I? There is more to the story, but im not gonna bore everyone with it..
All you can do man, is just forget about it and move on, 3.5 years is a lot to just let go of tho, its gonna be hard, but you can do it.