Opposite of tenancy?

The opposite of tenancy would be landlordship:

the condition or position of a landlord (Merriam-Webster)

Consider:

In 1415, Langenthal became incorporated into the territory of the Republic of Bern, but it remained under the landlordship and the low court of the monastery. (Wikipedia)

So your sentence would like this

It has been a pleasure staying under your landlordship.

However, I must say, this would be a rather uncommon statement. I would simply say:

It has been a pleasure being your tenant.

That does not mean, however, that you will find no instance of under your landlordship. Here's the proof:

It would also be beneficial for your rental business to get many good tenants under your landlordship. (Realtytoday)