Can I leave Thailand on an STV and return without losing my visa status?

Given your desired itinerary the STV visa doesn't sound like a good match. Maybe this would work for you instead: obtain a Tourist Visa (60 days on entry, can be extended for an additional 30 days), followed by a trip outside Thailand where you could obtain another Tourist Visa at a Thai Embassy or Consulate. You would receive another 60 days which is extendable by an additional 30 days when you entered Thailand again.

This would give you:

90 Days in Thailand

time outside Thailand

90 Days in Thailand

Note that you could also enter Thailand visa-exempt and get 30 days that could be extended for an additional 30 days.

The 30-day extensions of stay are applied for at any Immigration Office in Thailand for 1,900 baht and approval is practically guaranteed.

Look at your home country Thai Embassy website in Spain...

and you will read the specific requirements of the STV visa. Meet them and the visa is yours.

The STV is a “snowbirds” visa that allows a person to stay 9 months in Thailand.

In theory, you should be able to get a re-entry permit on the STV keeping your “permitted to” stamp alive.

Have I seen it before? No. But it’s your best shot.

There were only 5,000 people who got STVs last year.

The STV is NOT a multiple entry visa. Can use it only once on entry. Can be extended twice inside Thailand 90+90+90=270 days max stay and must leave.

STV was designed for those who wanted to spend up to 270 consecutive days inside of Thailand.

It's possible you could get a re-entry permit and return, but I haven't heard of anyone doing so.

If you can get a re-entry permit, you'd need to make sure you're back inside the country with enough time to get an extension before your entry expires.

Also if you're planning on leaving, you'd be wasting some money since you have to prepay your lodging to get the STV and extensions, so you'd be paying for something you're not using.