ikylm is a acronym or abbreviation of the phrase “I know you love me”. Usually used in a sarcastic way when someone is doing something minorly annoying or in a teasing way.
Sam: so do you like Trent??
Sophia: no
Sam: liar Sophia: I hate u
Sam: ikylm
The shortened form of the phrase "I kid you not" meaning the speaker is being serious/what they're saying is not an exaggeration. Usually only used when typing or texting.