“He has a Past” – sometimes that is out of our hands depending how we were rasied, and what type of yeshivahs our parents sent us too to hanging out in a wrong crowd. I personally believe in never judging a person on their past, but if you say that as recently as a month ago this person was still doing these things i think your friend should be alerted to the fact.
Rabbonim never like to break a shidduch and will say things to make it happen – i have seen it many times and couples are unhappily married after getting the peer pressure from teh rabbonim.
I would alert your friend and take it fromt there. I am sure everyone will have their own opinion.