I think as long as your account is in the HTC your calendar will be the one it syncs with. All you Google account info would have to be deleted and then your husband would have to enter his google acct. info. A master reset should take care of eleminating any of your information and give him a fresh system to work with.
Good luck, as I am always getting advice not giving it.
I need to know how to delete google calendar on my Htc thunderbolt, or how to delete all calendar items that keep showing up on the Htc thunderbolt that I gave to my husband. My husband does not want my calendar item reminders keep popping up on his phone.
Did you factory reset the phone before giving it to your husband? It sounds like your google/gmail account is still the primary google account on the phone. If your google/gmail account is a secondary account then you should be able to remove it by going to the settings > account & sync.
If it the primary google account, then you need to factory reset the phone and he needs to setup the phone with his google account.