I think that the crush she has on the game guy is not the problem. Rather, it's a symptom of a problem. The problem being that she's totally bored with both you and the lack of friends in her life.
You say that this game was the only thing you actually did together. What a sad indictment on your relationship! Do you never go out to dinner, or to a bar, a movie or a picnic? You don't shop together? Cook together? Laugh at stupid jokes together? You don't share interests or thoughts on domestic/world issues? Frankly, if this was the state of your relationship, it sounds like it was pretty much dead anyway. How did the relationship end up in this state?
As for her having no friends, what's that all about? Why does she have no friends?
If you want to fix this, she needs to be on board and work together with you to invigorate the relationship. But the question is "does she want to fix it?" It may be too far gone for her.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.