OP,
I am sorry that you are going through this. I know it’s not easy. Keep praying. I will pray for you, and this guy, as well.
Sometimes it’s hard to keep your own feet on the right path when you see someone straying from it–but remember that you can’t help them if you get pulled into the mire, too. Don’t compromise your morals. Stay on the right path, and if someone does reach out for your help, you can give them a hand getting back. If a guy is leading you away from God, either because he tempts you to do the wrong thing, or because you want to try and “save” him but he doesn’t want saving, then he’s the wrong guy.
I understand how difficult it can sometimes be to see someone you care about harming themselves, and wanting better for them–especially when they don’t seem to want better for themselves. The hardest part can be breaking it off and/or walking away when there is nothing more you can do. Unfortunately, I think that is probably what you will need to do this time. Your boyfriend already knew you would not approve of his behavior, or he would not have tried to hide it from you. But that was not enough to stop him from doing it anyway. You can forgive him (forgiveness doesn’t mean accepting the behavior), but you cannot solve this for him. And he doesn’t seem to want to solve it at this point–he’s giving excuses, not taking responsibility or trying to make changes.
He must make his own decisions and be responsible for them; you cannot force him to be honest with you, or to stop hanging out with the wrong crowd, or anything else. You can only decide what you will do, what you will accept. I would suggest not continuing the relationship, but that is, of course, up to you.
Remember, even Jesus didn’t convince everyone to follow Him. Many walked away, and though it saddened Him, He did not stop them. We mere human beings cannot force others to change their hearts, either.
You seem mature for your age, so I think you will understand what I’m saying here. Think about what kind of man you want to marry–by that I mean his personality, values, virtues. Does this guy’s behavior suggest that he would make a good husband and father? I know for some teenagers, marriage may seem a long way off, but if you begin now to only date guys who have at least some of those qualities you’ll seek in a husband, it becomes clearer, sooner, when the relationship is a poor fit, and easier to avoid guys who want you to compromise your morals. (It will also help if you think about the kind of wife you want to be, and work on nurturing those virtues in yourself.)
And remember that love does not mean tolerating bad behavior or sin.
May God bless you and watch over you.