Pronoun "mit dem" or "damit" in relative clause?

Answer 1

"mit dem" - preposition "mit" (with) requires Dative case -> therefore “dem” is the Dative form of the masculine definite article “der” that should be followed by a noun.

In contrast to “damit”, “mit dem” is a part of the relative clause which provides more information about the noun in the sentence.

They are usually introduced by the relative pronouns “who”, “whose”, “whom”, in this case “with whom”: “Das ist der Mann, mit dem (with whom) ich gesprochen habe.” – This is the man I spoke to.

“damit” - (in order to), (so that) – subordinating conjunction describing a purpose. For example: “Ich fliege nach USA, damit ich meine Englishe Sprache verbessern kann.” - I fly to USA, so that I could improve my English.