Selam aleykum
Well this is a really tricky situation, because a lot of actions with good intentions could sort of backfire. For example if you come on very strong saying: you're a sinner and you're evil and such, then the first thought that will naturally come to him is: "this guy is an idiot and doesn't know what I'm going trough, and as a result, you might even push him further away from Islam.
So some things to keep in mind while talking to him:
1. Try being supportive. acknowedge that he's going trough a rough time and try to guide him.
2. Try not to judge him. In Islam nobody has the right to judge his brother. However that doesn't mean we cannot judge an action.
So never say: "you're bad because of your actions"
Instead say: "that action is a bad action"
3. Try to avoid direct confrontation and argument, it won't help either of you. Instead focus on bringing him closer to Islam. If you can bring your friend closer to Islam, and teach him as much as possible of Islam, then inshaAllah he will realise his own mistake without anyone telling it to him. And be patient inshaAllah.
4. However if he is rebellious and you see that all your work is in vain, then at a certain point you might want to take your distance and focus your dawah on other people who are genuinely interested inshAllah.
And Allah subhana wa ta'ala knows best, may he make things easy for you and guide your friend; and may he forgive me if I gave wrong advice.