Thank you for asking me the question. Firstly you need to know that STD or Vdare infections that are transferred through sex (oral, vaginal or anal). Even though you are a monogamous couple you can risk STD. One needs to maintain proper hygiene both personal as well as oral to avoid bacterial growth that can cause infection. Even though in monogamous couple, it is possible that either of the partners had a relationship history in which they got the infection and which later developed to infect the other partner (in present).Most of the sexually transmitted infections have symptoms that are dormant for quite some timetherefore it cannot be concluded that monogamous couples cant risk STD or Vd.All  that a couple needs to do, even though being monogamous couple,  get regular medical checkups and test done to diagnose any symptoms of infection in both the partners. If one of the partners is found infected, the other partner should also get the test conducted, and a proper treatment procedure should be followed.  STD’s like Chlamydia, Trichomonas or Gonorrhoea are easy to spread and common sexually transmitted infections.  I hope your question is answered.  Wish you good luck. Take care.