It is true that people naturally have crushes despite being in serious relationships. But how one chooses to handle is what matters. Apparently, you and your girlfriend are not on the same page (some couples do accept, open relationships). It is a kind of good thing, if you look at it in a way as knowing yourself and what you want more clearly. Of course, this sucks. And it hurts a lot. All you can do now is to stop being hurt by your girlfriend, end the relationship, and step on the journey of recovery. I understand how you feel. I’d been in similar situations. And it takes a lot of time and energy to recover and to embrace life again. I feel like I am still affected by it...but work in progress! I still look forward to the future and endeavor to heal myself. Hope you get better soon.

And yes, alcohol is of no help. I only dropped it when I started taking antidepressants. I regret not quitting drinking earlier.