Questions: Guy's Behavior

So me and my friend are in this sports social group and this girl started too.
I like this girl and we went out to a football game together ( no a date). This girl is friendly personality and I read the signs wrong. So I text her afterwards and asked if she want to go on a date. She replied that she is not looking to get into a relationship ATM. I said OK no problem and we continued going to group.

That was to 2 months ago. I'm guessing my friend likes her too. The three of us go to football games together and they we always arrive together. My friend said that he is driving pass anyway so just collects her too.

So the other night I was driving pass this girls house and seen his car parked outside and the next day the car was stay there. Now I accepted that she is not interested in me and they can do whatever they like. So I started texting them both to try and see if they would admit that your were spending time together. They lied about spending time with each other. I meet them afterwards and said i was planning on leaving the sports group and do something else. They can be dating or are just good friends too.

My guy is a nice guy but is also a really take the hand/wind up person. And I'm worried he will take the piss and its hard enough seeing them together.

What should I do?