The correct option is
A never
Answer : A
Explanation:
Adverbs are words that modifies other words and expresses aspects of manner, time, place or degree.
Let us first understand what the words here provided to us in the alternatives mean:
--never: means "at no time" / "not ever" / "at no time in past or future"; it is a negative term and therefore it is used in affirmative/positive sentences to avoid double negatives.
--since: is used to refer to the time interval between a specific point in time and the time under consideration.
--for: is used to express a span of time.
--ever: means "at any time" / "all times"; it is used in negative sentences and quite
literally means the opposite of "always"; it is also used when asking
questions or conveying a doubt.
Adverbs that are used to assert / state / declare something are known as Adverbs of Affirmation.
And adverbs that are used to deny something are known as Adverbs of Negation.
"As much as" is used to refer to talk about two things that are equal either in amount or degree.
Here in this sentence the speaker is confessing his/her love to another person and using our emotional intelligence we can safely assume that that person loves only the person to whom he/she is confessing and has not loved anyone else as much.
And to express that we have to use an adverb of negation (denying loving anyone else as much).
Thus grammatically the most suitable word to complete the sentence here is "never".
Therefore the correct complete sentence is:
I have NEVER loved anyone as much as I love you.