New and Confused - ruining my life?

Hey all,im pretty new to these feelings. I'm 25 and been living the straight life for a long time. few years ago I've had an encounter with a guy and it did satisfy some curiosity but at the same time brushed it off.Been with my SO(girl) for 5 years now, moved across country together. We have a very stable lifestyle, not engaged and no kids, both professionals and trying to advance our careers.I've experimented some more a few months ago (yeah i know i shouldnt be, but thats my burden) and over time just thinking about my experiences. I'm confident that I am bisexual here. I have no idea what to do cause my SO is my best friend of my life but I feel like I'm living a lie if I stay with her. She would be devastated more over the fact that I'd be bisexual than the fact that I cheated on her with a guy (which to say, both bits of news will devastate her).I feel like i should leave. but I just cant. Shes my best friend still and we stuck out through a lot of shit thick and thin together. Also it would cause us both to be financially unstable and ruin our dreams together.I just dont know what the fuck to do. This may be just more of a rant than anything but i just need to tell someone. I have no one to talk to.