why do i speak spanish better than i understand it?

Have you had a hearing test recently? Quite often a hearing loss in just a specific tonal area can cause this. It doesn't particularly affect your understanding of English, since you are a native speaker and can pick up all sorts of clues to what's being said even when you hear it imperfectly. But it sure messes up your understanding a foreign language.

I found this out a few years ago. Suddenly, instead of my comprehension of Spanish slowly increasing, it began decreasing. I had my hearing tested and found out I had a very definite hearing loss. By purchasing some pretty cutting-edge, 32 channel, digital hearing aids, my comprehension came right back to where it had been and has been increasing (slowly) ever since.

I would be happy to recommend the company I bought the hearing aids from, as they sell a remarkable product at a remarkably low price. PM me if you're interested. I get no commissions, as I am in México and they are in Pennsylvania.

Actually, it's quite common. You know what you want to say and it's just a matter of remembering the right words. When people talk to you, you have to listen for what they're saying, understand the words and then translate them, in a short period of time. Also, people have varying accents which may differ from what you are comfortable with. It might not even be enough of a difference for you to tell but your ears do. My husband is one of very few people who understand others better then he speaks. It makes for interesting conversations when we travel since I also speak better then I understand. Also, speaking in a second language can make one nervous which causes your brain to not process the information as quickly.

I have been living in latin america for a couple years, currently in Colombia.

Where did you live before moving to Colombia? It seems to me that people along the Caribbean coast, both in Colombia and Venezuela, speak a Spanish that can be difficult to understand until you become accustomed to all the dropped or swallowed consonants.

I tutored English to immigrants, and one of my greatest challenges was to get a Colombian student to pronounce the consonants in English words. He said a word that sounded like SAW-tie, and I told him that hardly any native speaker of English would know that he had just said sometimes. His swallowing of consonants was more or less typical of people from his part of Colombia, where you would be likely to hear PA for para, LEE-toe for listo, etc.

The suggestion of mazgringo that you have your hearing tested is also a good one. I have aged into the hearing-aid group of older folks, and how I became aware of the beginnings of a hearing loss was when I mistook vibe for five. I thought that I needed a new television set (I heard the word in a commercial), but the problem continued even after I bought a new set. Now I wear a Phonak-brand hearing aid in one ear. I don't know how many channels it has, but it is digital, and the particular one I have was in the midrange of Phonak's products.

re: hearing loss
The very high frequencies are the first to go. If you're missing F, S, T, K, that could be the problem.

Without comparing with the others, speaking the language is you having control of what you want to express, at your own pace and comfort, whereas comprehending someone else's speech is beyond your control and requires much more effort? Just my two cents.

It's also a question of synonyms. To express yourself you need to know only one way to say it, but to understand you have to know also other ways to tell the same thing. Though this doesn't really explain why others understood better than you. It could be simply that they have a better ear for languages?

Watch telenovelas.

yes... the easiest way: telenovelas...