"My ex was sometimes really annoying."

Translation: Mon ex était parfois vraiment énervante.

[fH6lclhu]

Why "enervante" (feminine) is correct when "mon ex" is masculine? Is it because "ma ex" would be wrong?

[Rlando]

Because ex starts with a vowel, you use "mon" even for a female ex. The gender becomes clear only because "énervant(e)" is different.

Similar with the pronunciation of "mon ami" and "mon amie". In this case the spelling is different for a male and a female friend, but you can't hear it because "amie" stats with a vowel so also uses "mon" instead of "ma".

[Paul_in_Victoria]

Is it wrong to use "ennuyeux" in this context?

[Denise407335]

ennuyeux means boring not annoying

[maxekmek]

Agreed, "je m'ennuie" = "I'm bored".

[NiKolaasss]

The first meaning of "ennuyeux" is boring but actually, "ennuyeux" in French can also mean "enervant" so I think it should be accepted (from a French Native)

[rose830046]

Yes, several translation apps suggest ennuyant for annoying

[carcs1]

Can you use "quelquefois" for "sometimes"?

[Denise407335]

Duo accepts quelquefois in the following word order:
Mon ex était vraiment enervant quelquefois

[Balla583491]

parfois et vraiment two adverbs together . What is the rule on which adverb comes first in a sentence?