You can't make his choices for him but the red flags are there. Why would someone in true recovery want to date or be firends a drug dealer? How will you know if he brought drugs into your house? Unless she holds him down and forces him to relapse, she isn't to blame. I know it can be hard to NOT to blame the dealer, I know I have often struggles with that myself.
Buckle up, protect your heart and belongings.....this may just get rocky. I pray I am wrong!
Either way, my prayers go out to you and your son!