If a preposition is used with the relative pronounA part of speech that refers to or stands instead of a noun. E.g.: Who do you think I am? ("you", "I"), this preposition can either precede the pronoun or follow the verbA part of speech that expresses an action or a state. E.g.: John seldom plays tennis.. In the second case we can use the same pronouns as when the pronoun is in the objectA person or thing that is affected by the action of a verb or involved in the result of an action. role. Otherwise we use whom or which.

The house in which the famous poet was born is now a museum.
The house which the famous poet was born in is now a museum.
The house that the famous poet was born in is now a museum.
The house the famous poet was born in is now a museum.

Suzanne, with whom I am in love, got married yesterday.
Suzanne, who I am in love with, got married yesterday.

At which point (when) and in which case (if so) are used in non-defining clauseA group of related words containing a subject and a verb.s.

I watched the match until the end of the first half, at which point I decided to go home.
If there is a fire, the alarm will go off, in which case leave the building at once.

Pronouns used in non-defining relative clauses
Relative clauses WHAT and WHATEVER