Do the statements: "I see you are very happy to be with a man" and "There are many men in this program, so you should pursue them and affirm their words," constitute slander that necessitates expiation?

The mentioned statement does not constitute slander (qadhf), because slander is the explicit or implicit accusation of another person with indecency. However, it did contain an offense, and the obligation is sincere repentance and seeking forgiveness, unless one fears a greater harm, in which case reminding with good deeds and frequent supplication will suffice. One must be cautious of mixed communication groups due to the temptations and problems they entail. Allah the Almighty says: "O you who have believed, do not follow the footsteps of Satan. And whoever follows the footsteps of Satan - indeed, he enjoins immorality and wrongdoing. And if not for the favor of Allah upon you and His mercy, not one of you would ever have been pure; but Allah purifies whom He wills, and Allah is Hearing and Knowing." (An-Nur: 21).