If this is his first time going to prison/jail, there is cause for concern. If you can report his suicidal thought to someone, even the police, do so.
And remember, your friend was looking for an underage girl. That is a crime.
If he can take responsibility for his actions AND get help to explore and deal with his attraction to underage girls, he could get through this and move on to have a good life, not easy, but it is not the end of the world that it seems to be right now. Be glad he was caught at 20. And hope he did not have multiple victims before this attempt. Whether you maintain contact is up to you. If you choose not to, I would tell him why (sometimes the consequence of our behaviors is a loss of friends). If you do, I would be clear in not condoning or expressing sympathy for the "set up". He will not be able to look at what he has done if he can get away with "they framed me"---his intent was clear, as you relate the story.