If I take a bath in apple cider vinegar (diluted) after he ejaculates in me does this cut the chances of bv?

No. Bv is naturally in your vagina, along with "yeast." when one or the other gets off balance, the other will 'over grow'. People think of BV and yeast as infections, but they are really just overgrowth of something normal. The fishy smell after intercourse (sex) is as much the semen as it is you. Use condoms to help with that and for safer sex! if you need treatment for bv, see a doctor 1st.