You should consider your boyfriend's feelings and inform of the whole situation, he deserves to know the truth. If you have lost interest in him you should not lead him on any longer. Love can be complicated and people fall in and out of love every single day. If the tables were turned you would not want your boyfriend to do that to you. You have to really evaluate yourself and be sure if the relationship between you and your best friend worth becoming more. Good luck with your situation and hope everything works out for you.

You should tell him how you feel. Even if he is your ex boyfriends best friend, your ex is your ex for a reason. If he cheated on you or anything like that you don't owe him the courtesy of telling him you like his best friend. It sounds insensitive but sometimes you gotta forget about other people's opinions and live your life. If you don't follow your heart you could be asking "what if...". It sounds like you feel like you would be hurting your ex but if its over between you two its over. And you can still be civil to your ex. good luck with your situation.

To the first answer hes my ex boyfriends bestfriend

to the second answer thanx but im not worried what my ex boyfriend think the boy that i like is worried about it because they r friends