One of my best friends gave me her boyfriend .?

so if i get this right your friend was dating your now boyfriend but broke up and the two of you got together. She is dating his best friend and you guys used to hang out in a group. Now the group split and the two couples are off on their own. Your friend and her bf are more intimate than you and this david guy. Why would it go wrong? the only thing i can think of is david might want to move faster to keep up with his friend but other than that no i don't feel anything will go wrong.