I've been with my girlfriend for almost 4 years. I met her at work and we hit it off immediately. At the same time I started seeing my girlfriend, the most beautiful woman i've ever seen started at the same job. At first, it was very innocent, just talked about work. After about 2 years, something happened and her and I started to become more and more flirty. I will readily admit that I did try to take the flirting a little further, and she was very into the idea but it just never happened. While nothing had initially happened between us, we would talk throughout the day, including some text messages at night. As time went on, we started to become best friends. She started to come to me with her personal issues and really opened up to me and visa versa. I was still happily with my girlfriend but would think about this other girl. It was always "I wonder how she is doing" rather then lusty thoughts that would normally occur with people in this situation. I started to realize as time went on that what I was feeling for this other girl might not be a crush. The months went on and the feelings grew stronger. About a year and a half ago, I got a call from this girl asking if I could come over, she really needed to talk about something and she felt like I was the only one who could understand her. One thing led to another and we slept together. Being a 28 year old man, cheating is never something I've done nor is it something I ever thought was excusable. But she had me after that. I tried to meet up with her just for dinner or a drink and was very clear that I wasn't trying to have more sex. We had dinner a couple of times and I can literally say they were some of the best nights of my life and we never slept together again. 90% of the time, she would turn me down and I do understand but it has weighed on me; there is a complex that one gets when constantly turned down by someone who seems to love having you around.
The conversations between this other girl and I have become more intense in the past year and a half, and we tell each other things we could never say to anyone else. I do love my girlfriend but I love this other girl as well. In fact, I've never loved anything as much as I love this other girl. She is my soulmate and my best friend and I would literally do anything in the world for her. I'm not sure why her and I have never had a conversation about what her and I could be, but we never have. I can't help but think she is absolutely terrified about what has happened between her and I over these past couple of years. She has admitted that she has pulled away when things have gotten very real, but she says she can't really explain why. There is like this dark cloud over her and I, we can say anything in the world to each other except how we really feel about each other.
I know how wrong it is to have a relationship with a girl that isn't my girlfriend like this, and the guilt has weighed heavily on me. Things have gotten progressively worse between my girlfriend and I and I do know that the relationship is destined for failure. With that being said, my girlfriend left my job a month ago, and I recently put in my notice of resignation. This brings me to my dilemma.
I feel very scared about what will happen with this other girl. I know I am going to miss her like crazy. My question is: what do I do? Do I need to tell this girl that I am absolutely in love with her before I risk never seeing her again? Or do I just take it for what it is: she simply doesn't feel the same way, move on with my life? Please help.