I had the urge to go down on my good friends girlfriend and I acted on it.
Why did you give in on the urge?
I find her attractive, there is no deep meaning in it it just happened.
It is wrong to sleep with your best friends girlfriend. You can ruin your friendship if they ever find out what you did.
Is it really wrong?
Absolutely it is. You're betraying your friend and ruining his relationship with his girlfriend. I recommend not doing it again because this will probably end up poorly for you.