I feel like I'm ditching my best friend for a guy, but.... the guy is gay.... yeah, interesting, eh?

Why dont you tell your gay friend how you felt for him? See how he will react on it. If he ditch you then thats bad for you. But if he will tell you that he feel you as a friend then you can continue your relationship and stop your daydreaming. Introduce your gay friend to your girlfriend and you will be a circle of friends, she might like his company also. On that way you will be much happier on their companies without ditching anyone.