If you want to stay in Spain long term, there's some good news - Spain wants you to!
If you've been bitten by the Spanish lifestyle bug, there is unfortunately no treatment - but long-term rehab is possible by actually moving to Spain.
Two recent decisions by authorities in Spain have made it easier to stick around in Spain. If you want to move here, Universities in Valencia are now offering degree courses in English. The move is intended to make Spanish students more employable, but the move will likely have the advantage of bringing in more foreign students.
Another move that will encourage long-term stays is the new policy that Spain will offer residency to foreigners buying homes in the country. If you can spend more than 160,000€ on a property in Spain, the government will allow you to stay in the country indefinitely. A similar offer has been made by Portugal and Ireland, but the minimum spend required is a lot higher in both cases.
If you don't plan on moving to Spain for quite so long, remember that if you are an EU citizen, you can stay in the Spain without the need for a visa. Visitors from other countries have some restrictions - Americans, for example, can stay for 90 days out of every 180 in the Schengen zone, of which Spain is a part.
If you want to spend a few months in Spain, how can you best occupy your time? You can't just party the whole time or visit museums every day!
A popular activity is the Camino de Santiago, a series of pilgrimage routes that lead to Santiago de Compostela (and beyond, if you feel up to it). Start at the French border and the walking will take at least a month. Read more here: Camino de Santiago Guide
Or why not learn Spanish? In three months you can easily get to a good conversational level or higher. (I reached the top (advanced) class from complete beginner when I studied at CLIC in Seville). Read more about Learning Spanish in Spain.