Your dr needs to know anything that could affect your pregnancy. This includes your sexual history if this dr doesnt know your history. Just remember he/she isnt there to judge but just to help you carry and deliver a healthy baby. With regards to the father, the only question my dh was asked was about ethnic orgin because some carry genes for certain disorders. Just answer any and all questions the best you can. Women have been having babies without men involved for decades so dont stress about it.
Congratulations! Hope you have a happy and healthy 9 months.