Rules for dating friends of exes
The fact that you have waited 5 months now makes your honesty not as relieving or effective in helping to diffuse the situation.
He is going to feel like you went behind your back, have been sneaking around (which you already admitted you have done), and that you are not a “true best friend.” What you need to do, is to think critically about why you did not tell him in the beginning, and why this situation is different perhaps than a similar one- say, one where you date your best friend’s ex-girlfriend too soon after they break up and he is still in love with her, or you are the person who your best friend ex-girlfriend is cheating on him with.
I agree with Rebecca and Drew, but also have a few things that I think you should consider.
First of all, it definitely is not a great thing that you have been dating your girlfriend for 5 months now and have not told your best friend yet.
Secondly, you want to make sure the individual you’re pursuing is really worth the risk.
Put yourself in your friend’s position and examine the situation.
The reason that this is different is that some time has passed since your best friend’s relationship with her so it should be well over with, and that you knew the ex-girlfriend (your current girlfriend) first, and had a friendship there that was healthy and in fact always had some potential.
All that being said, I think you need to sit down with your best friend and with your girlfriend and explain everything from top to bottom, including why you didn’t tell him in the beginning, which hopefully is because you were afraid of hurting him and just didn’t know how.
If this ever happens again, remember that honesty, in the beginning, is the best strategy for dealing with any problems or drama in life.If there was a black and white answer, it would be that you don’t date the ex.