Example sentences:
Susan didn't enjoy the date, because it was too __.
Mary's marriage has become __. She's the only one speaking.
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Sign up to join this communityExample sentences:
Susan didn't enjoy the date, because it was too __.
Mary's marriage has become __. She's the only one speaking.
"One-sided" is common usage and would work in both of your examples; however, its usage is broader than just about conversations -- though it is often used to modify 'conversation' (see many results for 'one-sided conversation' google search, or http://www.basicinstructions.net/basic-instructions/2009/4/29/how-to-end-a-one-sided-conversation.html).
If you wanted to avoid usage of one-sided, your options for a one-word solution might be limited or awkward. There are some idioms for what you describe, such as:
You may also consider use of the word "monologue," which has the usage "a prolonged talk or discourse by a single speaker, especially one dominating or monopolizing a conversation" (http://www.dictionary.com/browse/monologue).
One could say that the conversation was lopsided:
Lopsided:
ADJECTIVE
1 With one side lower or smaller than the other.
‘a lopsided grin’
1.1 Disproportionately weighted in favor of one side over another.
‘a lopsided competition’
https://en.oxforddictionaries.com/definition/us/lopsided
If it suits, you might also explore concepts such as unbalanced or uneven.
Unilateral is another possibilty for your second example:
adjective
(of an action or decision) performed by or affecting only one person, group, or country involved in a situation, without the agreement of another or the others.
(from https://www.lexico.com/en/definition/unilateral)
It is simply a highfalutin way to say onesided, which was already given.
monologue:
A monologue is a speech delivered by one person, or a long one-sided conversation that makes you want to pull your hair out from boredom. The Greek root word monologos translates to “speaking alone,” and that's a monologue: one person doing all the talking.