CALENDARS- iPhone and google not synching correctly

The syncing used to work correctly. That was until I started watching videos on all the latest and greatest tips and tricks for iPhones. the google email account is listed on my iphone as a mail calendar account and it synchs across all events. I must have done something, and I messed it up. Now, when my husband sends me a calendar invite, it never shows up in my iPhone calendar inbox. It does show up in my Gmail inbox as a message and I open it up . I select yes to accept the invite, then at the bottom, I once again select yes to add it to the calendar, and it only adds it to the Google Calendar, and that never syncs with the Apple Calendar anymore. And we only use the Apple Calendar as our only calendar that way we can see each other's appointments. but now with his invites not showing up in my inbox I have been trying to remember what is happening in both calendars and it is driving us both crazy and we need it to work again, to save our marriage!