I started lurking here in 2003 when I was a BGF. I was so intimidated because I saw men and women who were 5, 10, 20,40 years into marriages who were betrayed. I felt I didn't belong here and a whiner simply because I was "just" a betrayed girlfriend in a long term relationship. No children, not many years of involvement so I had no room to be sad. You're entitled to your feelings.
Know what? Infidelity can color your entire life regardless of where you are in your development. Yes I was a young 20 something but I learned so much from the people here. Cheating hurts at any age. I saw so much wisdom here from many people. It may hurt but it's helpful. Take the good and leave the rest. Many uplifting and wise posts stopped me from indulging in dangerous behaviors.
Why am I still here after all these years? Because infidelity left it's mark on me, as well as my sweet DH who was also a BSO before we met. This is a site full of encouragement, honest yet sometimes harsh and kind words. Listen to the people here. Just do it. Even my therapist claimed this was a good place.