Это дом, у которого мы встретились.

Here у которого means by which / at which / near which.

The whole clause у которого мы встретились literally means something like by which we met or at which we met, with which referring back to дом.

So the structure is:

• дом = house
• который = which
• у которого = by/at which

In more natural English, this becomes the house where we met or the house by which we met, depending on the exact context.

Because the preposition у requires the genitive case.

The basic dictionary form is который. But after у, it must change:

• который → nominative
• которого → genitive masculine/neuter singular

Since дом is masculine singular, the relative pronoun must match it in gender and number, and then take the case required by у.

So:

• дом = masculine singular
• у
  • genitive
• therefore: у которого

Russian relative pronouns like который agree with the noun they refer to in:

• gender
• number

but their case depends on their role inside the relative clause.

Here:

• дом is masculine singular
• so the pronoun must also be masculine singular: которого
• but its case is genitive because of у

This is a very important Russian pattern:

• gender/number = from the noun being described
• case = from the pronoun’s job inside the clause

In this sentence, у means something like:

• by
• near
• at

It often indicates location next to something.

So у дома means by the house / near the house.

That is why у которого мы встретились gives the idea by which we met or near which we met.

Russian often uses у for being near a person or thing, not necessarily inside it.

Because у которого мы встретились is a relative clause describing дом.

Russian normally separates this kind of clause with a comma:

• Это дом, у которого мы встретились.

This is similar to English writing:

• This is the house where we met.

In Russian, relative clauses introduced by forms of который are typically set off with commas.

Это дом and этот дом are different structures.

• Это дом = This is the house / This is a house
• Этот дом = this house

In your sentence, это is being used in an identifying statement:

• Это дом... = This is the house...

If you said Этот дом, у которого мы встретились, that would not work as a normal complete sentence by itself. You would usually need more, such as:

• Этот дом — тот самый, у которого мы встретились.

So here это is correct because the sentence is presenting or identifying something.

Because дом is the main noun in the statement Это дом.

It is the noun being identified, so it appears in the nominative:

• Это дом = This is the house

The relative clause after it does not change the case of дом itself. The clause only adds information about the house.

So:

• дом = nominative, because it is the main noun of the sentence
• которого = genitive, because it depends on у inside the relative clause

Yes, very often Russian speakers would say:

• Это дом, где мы встретились.

That is a very natural way to say This is the house where we met.

The difference is that у которого is more literal and specifically suggests by/near the house, while где simply means where.

So the two can be close in meaning, but the nuance is slightly different:

• где мы встретились = where we met
• у которого мы встретились = by/near which we met

If the meaning is specifically outside the house, near it, then у которого makes that clearer.

It is grammatical, but in everyday speech many speakers would more naturally say:

• Это дом, где мы встретились.
• Это тот дом, у которого мы встретились.

Your sentence is understandable, but у которого can sound a little more formal, explicit, or bookish than где in this context.

Also, if the speaker means that specific house, adding тот often makes it sound more natural:

• Это тот дом, у которого мы встретились.

Because the subject is мы = we.

Russian past tense verbs agree with the subject in:

• gender if singular
• number

Since мы is plural, the verb is plural:

• мы встретились = we met

Compare:

• я встретился / встретилась = I met
• он встретился = he met
• она встретилась = she met
• мы встретились = we met

Because here мы встретились means we met each other.

Russian встретиться can work in different ways:

• Мы встретились. = We met. / We met each other.
• Я встретился с другом. = I met with a friend. / I met a friend.

So when the subject is plural and clearly refers to the people meeting one another, Russian often does not need с кем-то.

In your sentence, the focus is on the place of the meeting, not on whom they met:

• у которого мы встретились = by which we met

Yes, Russian word order is flexible, but the neutral order here is:

• Это дом, у которого мы встретились.

That sounds straightforward and normal.

You could move words around for emphasis, but that would usually sound marked or stylistic. For example:

• Это дом, у которого встретились мы.

This puts unusual emphasis on мы and is not the normal choice in ordinary speech.

So for learners, the best pattern to remember is:

• Это + noun, + relative clause

The pattern is:

• Это + noun, + preposition + form of который + clause

In this sentence:

• Это = this is
• дом = the house
• у которого = by/at which
• мы встретились = we met

So the sentence is built as:

• This is the house by/at which we met

This is a common Russian way to form relative clauses:

• Это человек, с которым я работаю.
  = This is the person with whom I work.

• Это город, в котором она живёт.
  = This is the city in which she lives.

• Это дом, у которого мы встретились.
  = This is the house by/at which we met.