Just like everyone said... Have a talk with him. Remember that you were close with him before you knew her... It's a guy code "Bros before hoes". Make sure that he knows your intentions... and make sure you gain that respect you should get from him by approaching him about it. And if he gives you any terms or conditions... respect them. Don't ditch out on him either... hang out with him regularly and try to spend time with her too. This could be a potentially awesome situation for you... You could have the parents on your side... meaning if this girl ever decides to split on you... her parents are going to be cool with you over any other guy... And plus... it's always to know the person that you're with has cool parents that you can hang out with. Awesome man... congrats.