No! No! Not OK! Hear now, children, the wisdom of the elders...fine, so I'm 18, but mentally I was born at about 35, so I think I still qualify.
It's not OK. It will not be OK a month from now, two months from now, a year from now. The ONLY TIME it will become OK is if you grow up, stop associating with this guy, forget that he ever existed, and then by some remote cosmic miracle That Slut From Whatever Grade You're In finds her way back into his life and they get married. And even then, I wouldn't attend the wedding.