I'd like to add a couple Pastoral notes to Eric's very correct response.
So long as he went to Confession and the priest didn't tell him he had to turn himself in as part of making restitution, then nothing further is required. A priest will rarely, if ever, require someone to turn themselves in as a condition of absolution. I've only heard of it mentioned when the person has committed murder. On occasion when the sin involves theft, then the priest might require that the person return the money.
To further put your mind at ease, let me briefly share my story.
Before I surrendered my life to Jesus, I was not only a cocaine addict, but dealt in very large quantities of cocaine and other drugs. The Lord immediately delivered me from the addiction. I actually wound up as a Protestant Minister but when I came back to the Church, I confessed the sin of doing and dealing in high volumes of drugs.
God had already forgiven me and restored my life some six years earlier and started using me for His purposes. My testimony is public. The local police now know, what I know behind the scene in the area of dealing drugs, not because I turned myself in but because I openly share God's work in my life, miraculously delivering me from addiction and from dealing. I've spoken at various groups on this subject including Drug Rehab programs. I've told friends of mine on the Police force, that I'd gladly speak to any group they feel could benefit from my story. So if the police weren't interested in arresting me, a guy who was dealing in kilos at a time, I'm sure your boyfriend is safe. The police aren't interested in prosecuting people who have turned their lives around.
That said, don't get me wrong. I'm not suggesting your boyfriend needs to tell the police about anyone else involved in his crimes. I chose to do so because I believed it could help others and it's a powerful witness of what God can do in our lives. I take exactly zero credit for my life turning around. It was all Jesus. All I did was to accept His forgiveness.
Further, I'm virtually positive no priest will tell him to turn himself in as condition of absolution so don't stress out over that.
Remember St. Paul was a murderer who went around killing and persecuting the earliest Christian converts, who were Jews.
So God writes straight with crooked lines. Not only has He forgiven your boyfriend, but He has fully restored him as if he never committed that sin. That sin, becomes part of your boyfriend's testimony that, if he so chooses, he can share as powerful witness of God's forgiveness. Again, that is his choice and it's also up to God to call him to share the story.
You have nothing to worry about in terms of him being forgiven. God isn't in the business of finding reasons to send people to Hell. Quite the opposite: He suffered, died, and rose from the dead, to free us from the punishment due to sin, so that we might have eternal life and fellowship with Him.
With respect to your OCD , I would highly recommend that you meditate on Romans Chapter 8 — it's a very powerful chapter. Meditating on such passages will help renew your mind and way of thinking. It will help you with both this particular issue, and your OCD, which I suspect may also manifest itself in scrupulosity . . . which is an obsessive concern that you are sinning and you aren't forgiven.
I hope this helps,