"My friend comes to my home."
Translation:मेरा दोस्त मेरे घर आता है ।
It should be मेरे because it is in the oblique case, i.e, followed by a postposition (corresponding to preposition 'to' in the English sentence) which in this case is implicit.
When in the oblique case, some nouns and the possessive pronouns referring to them change form. For possessive pronouns, this change is limited only to those that precede a masculine singular noun. So, मेरा becomes मेरे, हमारा becomes हमारे, उसका becomes उसके etc when it is followed by a masculine singular noun which in turn is followed by a postposition.
The ‘implicit’ part is key. Others have referred to this as the ghostpostition, since it’s operative grammatically but not written/spoken. So ghostly! What a बुध बंगला !
Is दोस्त always masculine, or can it be feminine?
मेरी दोस्त मेरे घर आती है was rejected for me.
मेरी दोस्त मेरे घर आती है। is perfectly acceptable in common use. However, now that I think about it, using दोस्त as a feminine noun does seem tricky and I don't know what nitpicky grammarians would have to say about it. (For instance, how would you phrase it when talking about multiple female friends?) But grammar woes aside, no native speaker would think twice about using दोस्त as feminine and Duo should certainly accept it.
You might be familiar with 'prepositions' in English such as 'in', 'from', 'of', 'on' etc. These words come before noun phrase that is their object. For example, 'on the table', 'from Delhi', 'at night' and so on.
In contrast, Hindi uses 'postpositions' (like के, से, का, पर etc) which serve the same purpose but come after the noun phrase that is their object. Eg: ' मेज़ के ऊपर', 'दिल्ली से', 'रात को' and so on