I speak Spanish at an intermediate level, and I'm attending an intensive course with a lot of grammar (the finer points of using ser & estar, the subjunctive etc.). I'm considering starting learning Esperanto. My problem is that quite a few Esperanto constructions look to me as broken Spanish.
For example, Esperanto uses the verb "estas" in all persons, but it resembles Spanish "estás", which is only used in the second person singular. Moreover, Esperanto uses "estas" in contexts where in Spanish a form of "ser" is appropriate, and not "estar".
Another problem is that the Esperanto article is "la" (which looks the same as the Spanish feminine article), but all nouns end with -o (like many Spanish masculine nouns).
I'm pretty sure that if I read more Esperanto, I will get used to it, and all these constructions will stop appearing as strange to me. But here is the point: can it also interfere with my ability to tell grammatical from ungrammatical Spanish? My biggest concern is that if I often see sentences such as "vi estas la amo de mia vivo", then Spanish sentences such as "tu estas la amor de mi vida" will also start to look correct. For now, the Spanish sentence looks completely wrong to my eyes, and I would like it to stay that way.
Can learning Esperanto interfere with my Spanish? Should I wait until I get to the advanced level with Spanish, or am I worrying unnecessarily? I'm most interested about experiences with Spanish and Esperanto, but if you have experience with interference (or lack thereof) in another similar language pair, you are also welcome to post an answer.