If you're partner also has Google Mail, this is you best option for a shared calendar.
Go to the Google site and go to your calendar. Create a new calendar and call it something business like. Under the settings for that calendar you can choose to share it, either as a view only or as something your partner can also update. You'll be able to send your partner an invitation from there. I can't tell you much more than that, because I've never actually shared a calendar. Only noticed the settings while doing other things.
Once you have the calendar working via Google in a browser, you can add it to your iPad.
If you have your iPad set up as a standard GMail account, you'll need to re-add it as an Exchange account. Either go into your GMail account and turn off all the sync services, or just delete it. Your data is safe on Google's servers, so don't worry about it disappearing off you iPad. You can get it back easily.
To set up the Exchange account follow these instruction.
Google Mail as Exchange
Set Up Your Apple Device for Google Sync : Google Sync (ActiveSync) - Google Mobile Help
Be sure to follow the last link on the page to set up your extra calendar. You have to visit the m.google/sync site from you iPad to do perform this last step. If you already had your Google account set up as Exchange, this is the only step you'll need to do.
Throughout the process you need to pay close attention to the remove events and merge or overwrite event notifications. If you have events stored locally on the iPad that are not in a gmail or hotmail calendar, be careful not to overwrite them when adding the Google account again.
If the events you wanted to share were on the another calendar, you can now move them. Just tap on them, edit, and choose the new calendar.