I think you misunderstood the sentence.
A boy: I'm your boyfriend, Ji Hun.
B girl: Since when do you become my boyfriend?
It means B girl is not happy and B girl tell A boy that A boy is not my boy friend.
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A purist may argue that there is no need for since - quite simply When did you become my boyfriend? would suffice. But having Since when DID you become ... is a conventional and therefore acceptable pattern. The best way to deploy the word since imo, is to use the verb to be: Since when are you my boyfriend?. When you say do it implies and ongoing procedure or condition eg. the condition of liking something, or doing or practicing something. To have become something (eg. someone's boyfriend) implies an exact point in time, hence the past tense did is the correct usage. YOu may include the word START and then the DID as well, to all your examples: Since when DID you START(doing your make up/liking soccer/ to like soccer). The exact point in time when the change took place is now implied more directly.
But, hey - I am not a master in English ;-) I just have a Bachelor's degree.
No - I assure you. I do understand English. You need to say, Since when are YOU my boyfriend? or Since when did YOU become my boyfriend?. The inflexion needs to be as though it is an interrogative question also i.e. rising inflexion on one word or rising at the end as though you wish the listener to answer a confirmation or deny your implication (that he is NOT your boyfriend).