Because mi here is a possessive adjective, meaning my.
Compare:
So in this sentence, the correct form is mi without an accent mark.
Spanish often leaves out subject pronouns because the verb ending already gives information about the subject.
Vive is the third person singular form of vivir, so it can mean:
Since mi ex is already the subject, adding él or ella would usually be unnecessary:
Vive is the present tense, third person singular form of the verb vivir (to live).
Full present tense of vivir:
So mi ex vive means my ex lives.
That is the most natural word order here:
Spanish often puts adverbs of place like aquí after the verb.
You could move it for emphasis in some contexts:
But the original version is the neutral, standard order.
The written accent helps show the correct stress: a-QUÍ.
It is a standard spelling rule. You simply need to learn it as aquí, not aqui.
Other common words with a written accent include:
No, not usually. In Spanish, b and v are pronounced very similarly, and neither is usually the strong English v sound.
So vive does not sound like English vee-vay.
It sounds more like:
This is normal Spanish pronunciation.
Yes, depending on context, mi ex can refer more generally to a former romantic partner, including an ex-spouse.
If someone wants to be specific, they might say:
But mi ex is very common as a general term.
Yes. The Spanish present tense can often correspond to either the simple present or the present continuous in English, depending on context.
So Mi ex vive aquí most naturally means:
But in some contexts, it could also be understood as:
Still, the default interpretation is usually the simple statement of residence: My ex lives here.
Yes, completely natural.
Mi ex vive aquí is short, normal, and idiomatic Spanish. A speaker in Spain would easily understand it and would not find anything strange about the wording.