Are you as overt about your faith, about your commitment to Jesus as one of his disciples as your friend is about his sin? We tend to talk about what most preoccupies and/or gratifies us. Does Jesus preoccupy and gratify you? If he does, that's going to come out in your conversation. Does it? I have found that when I am "salt and light," when I don't hide the light of my love for Christ, those people who are my friends are either drawn to that light or repelled by it. In either case, I need do no more than be open and free about my love of my Saviour and Lord to elicit one of these two responses. Be, therefore, the salt and light Jesus has called you to be as one of his disciples. As you are, a natural "weeding-out" process will happen with your friend. He will either be drawn to the Saviour you love and talk about all the time, or he will be repelled. But he will be the one who does the leaving or staying.
If King Solomon could be induced by the wicked influence of his pagan wives to forsake the wisdom God had given him, anyone can be dragged down into sin by those who love darkness. This is why the Bible is so clear about your situation:
2 Corinthians 6:14-15
14 Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness?
15 And what accord has Christ with Belial? Or what part has a believer with an unbeliever?
Ephesians 5:8-12
8 For you were once darkness, but now you are light in the Lord. Walk as children of light
9 (for the fruit of the Spirit is in all goodness, righteousness, and truth),
10 finding out what is acceptable to the Lord.
11 And have no fellowship with the unfruitful works of darkness, but rather expose them.
12 For it is shameful even to speak of those things which are done by them in secret.
1 Corinthians 15:33
33 Do not be deceived: "Evil company corrupts good habits."
Selah.