x2 is the Valentine (date/lover for the eponymous holiday) of x1; x1 is to go out on a Valentine''s Day date or otherwise be (ceremonially) associated with x2 for the holiday and festivities of Valentine's Day.
The proper Lojban ordering of the terbri (x1 then x2) is rather awkward to translate into English. The date need not actually be conducted or recognized; rather, the intent is there; additionally, it need not be official (as with longstanding romantic relationships). There is an implication of mild attraction or romantic partnering, but it need not be strong.