Experts are in agreement that Gardnerella vaginalis and Ureaplasma hominis are bacteria which are normally found in the adult genital tract and are not STI pathogens.  Tests for these to very common, normal bacteria are unfortunately included in many so called "comprehensive" STI screens and cause a lot of confusion.  In men there is no need to treat these bacterial. There is also no need to treat ureaplasma in women.  In contract, forwomen, on occasion,as part of a syndrome called bacterial vaginosis (BV), vaginal bacteria become unbalanced and there is overgrowth of Garnerella vaginalis, causing increased vaginal discharge.  When this sort of disturbance of normal bacterial balance in the vagina occurs, treatment of women with metronidazole can help restore the balance.  In such situations, there are good scientific studies which show that treatment of male sexual partners of women with BV does not improve restoration of balance, nor dues it prevent recurrence.  

I see no need for you to take the medications you have been prescribed.  There is also no reason for you to not kiss your GF because of the tests you describe.

I hope this information is helpful.  If any part of my response is unclear or there are additional questions, please don't hesitate to use your up to two follow-ups for clarification.  EWH