I don't know if your boyfriend is sincere; some people, I'm convinced, only use this as an excuse to keep using drugs.
But even if he is sincere, he's deceiving himself by thinking drugs will bring him closer to God. Yes, he may feel a sense of temporary peace when he's under their influence, but in reality what he's experiencing is only a counterfeit of true peace. Like the deceptive prophets of Jeremiah's day, those who claim drugs are the path to God "all practice deceit... 'Peace, peace,' they say, when there is no peace" (Jeremiah 6:13-14).
Only one path will lead us to God -- and that path goes through the cross. Our greatest problem is our sin, which causes a great gulf between us and God. Until that gulf is bridged, God remains far from us. But only Christ can bridge that gulf, because He came from heaven to solve our sin problem. Drugs, meditation techniques, good works -- nothing can bridge that gap, except Christ. The Bible says, "For there is one God and one mediator between God and men, the man Christ Jesus" (1 Timothy 2:5-6).
Pray for your friend, and urge him to face his need to repent of his sins and open his life to Jesus Christ. And if you have never given your own life to Christ, do so today. If your friend persists in doing drugs, however, face the fact that this will only bring unhappiness to your relationship. God has a better plan for you.