Nebicard is the brand name of a medicine called nebivolol. It belongs to a group of drugs called beta-blockers. One of the side effects of Nebicard is impotence; therefore unless there is no alternative, it should not be given to sexually active males.
It is not clear as to the reasons, which prompted change of medication from diltiazem particularly since you were doing well.
You can safely go back to diltiazem. It is desirable to take a slow-release preparation such as Dilcontin Continus XL 90 mg in order to achieve and maintain steady blood levels throughout 24 hours.