Need relationship advice

I ve been in a relationship with my girlfriend for almost 9 years. The problem is that I ve always had a huge crush in a female friend that i have known for far longer than my gf. I ve always known that she felt something for me too but we never said anything to eachother because one of us was always in a relationship. A while ago she broke up with her boyfriend and she told me a month after and we went out to a club i just wanted to cheer her up but we got really drunk and we had sex. I could not tell my girlfriend because i did not want to break her heart i told myself it was a drunken mistake and I wanted to continue the relationship but the truth is that I kind of fell out of love with her for the past year and the relationship turned in a habit. I continued to hang out with my friend i helped her a lot in the next few months as she had some problems but after that we ended up having sex again. After a while she told me that we cannot continue that because I have a girlfriend and I agreed and told her that I will decide what I want to do. I really wanted to try something with her but I was afraid that after such a long relationship both me and her would not be ready for something more than sex. I never told my girlfriend about what happened I guess I never got the courage and I did not want to break her heart. And now some time has passed I ve been feeling miserable both because I cheated on my girlfriend and because I never did anyhing more with my friend. I never really wanted to cheat I think I've done it because of the feelings that I had towards my friend for such a long time. We had some problems with my girlfriend I changed a lot of stuff and she never wanted to change some stuff that I wanted her to change. We don't fight a lot but the main problem is I've been falling out of love. Recently she told me that after a night out with her friends at a club she kissed with a guy and that she did it because I have lost interest in her. I kind of hoped that she would do something like that and that it would be an oppertunity to break up but and that I would be able to tell her that i cheated too but I thought that if I did not tell her than that it is best that I don't tell her and i just could not break up with her I told her that i have not been feeling the same and we decided to try and save the relationship. Two months have passed since than I have been more miserable than ever and I never really did anything for the relationship while she is really trying. I know that I should break up but I've never been good at relationships and showing my try feelings I am very shy and it is very hard for me because I really don't want to hurt my girlfriend but I know that the relationship has no future( she would never forgive me if i tell her that i cheated) and I feel really bad for cheating. On the other hand I know I have to tell my friend how i really feel but she started dating somebody recently and I feel she might get mad that I tell her something like that now after all that happened ( we stayed friends and we still hangout). I feel i might hurt her also as she is suffering from depression at the moment and i could not stand losing her too. I know that this is very complicated but I really need help because I don't know how to break up, mostly because I cannot get the courage because I feel really bar. I thought about going to a psychologist because I suffer from anxiety for the past year and a half and all of this is making it worse.