sometimes it's just plain hard

I've been doing very well despite T's and J's situation.  J appears to be doing very well but I know he isn't - as long as I know he's drinking.  He tells me he's doing fine and is now only drinking on weekends.  He's the one that came to us - telling us he had a problem, after all, since we didn't have a clue.  
T walked in this early evening (obviously stoned) to put on his bathing suit to go to the beach with friends.  I know that one of his friends' mom, that he was with today, has been trying to get  her 17 year old son into inpatient treatment.  And the other friends that were going with him to the beach? Two girls - one a 23 years old, and the other girl,  17.  I don't understand why the 23 year old would "chill" with these kids.  T used to date her younger sister when he was at his worst.  I really liked that girl and couldn't understand why she would want to be with our son, considering his "state".  Her older sister, that T and his friends have been spending time with is a college graduate with a teaching degree.  She sometimes comes to the house and picks him up.  I was told by another mom that she is an okay kid.  I'm sure she is but why?  Why is a 23 year old girl hanging out with a much younger group that uses?  Maybe she is........... but is good, like our middle son, at hiding it.