I think CP-V2. Because "A friend of mine is secretly in love with me" becomes:
"A friend of mine is secretly with me in love". Does that sound right to you?
This sentence isn't diagnostic of anything because there verb phrase is simple. It could be from a V2 language (of either sort) but also of an ordinary SVO language like English.
What happens to the order when you move "secretly" to front of the sentence? What happens when the sentence becomes a subordinate clause? Here are examples of each from a CP-SVO language, namely German.
"Ein Freund von mir ist heimlich in mich verliebt." (The order "heimlich verliebt in mich" is also possible although somewhat less common. Like your example sentence, this isn't diagnostic of V2 order.)
"Heimlich ist ein Freund von mir in mich verliebt." (V2. Cf. English "Secretly, a friend of mine is in love with me" with non-V2 SVO order.)
"Sie sagt, dass ein Freund von mir heimlich in mich verliebt ist." (V2 SOV--note how the inflected verb stays at the end, which is evidence for underlying SOV order.)
*"Sie sagt, dass heimlich ein Freund von mir in mich verliebt ist." (CP. The kind of movement allowed in main clauses isn't found in subordinate ones.)