The best thing you can do for your boyfriend is to help him find a good criminal defense attorney. No one on this forum will be able to accurately predict the outcome of your boyfriend's case given the limited information provided. However, as a general rule, if your boyfriend was on probation for a drug case and has been charged with new crimes, there is a very good possibility that his probation will be revoked. How much time he will have to serve on his probation revocation will depend on his sentence structure (i.e. whether the judge imposed but stayed a sentence or whether it was a withheld sentence).
Your boyfriend needs an attorney to defend him at his revocation hearing and to defend him against the new charges. Once your boyfriend hires an attorney, he or she will be in a much better position to advise you both as to the likely outcomes of his case.
Best of luck.