Q. Thank you for giving me your email this morning.
Soon after I married in 1984 my father bought a cemetery plot for myself and my wife in the…  We divorced eleven years ago and I had forgotten about the plots and when the separation agreement was written up it was left out.  Now her plot is still in her name.  I have not remarried and I was wondering is there a halacha that says I can’t be buried next to a woman I’m not married to?  
Thank you.
A. Poskim disagree if non related men and women can be buried in adjacent plots.
Igrois Moshe (Y,D, 1:241) considers that it is a great “bizayon” or shame to bury a man next to a woman that was not his wife, or a woman next to a strange man. He mentions that it is an established custom not to do so and permits the removal on the buried to another site. (See also Mishne Halochos 13: 222).
However, Kol Bo (p, 179), mentions that there are congregations where the bury men next non related women. He quotes Hedras Kodesh that this was the common tradition in Levuv.. He also cites Imrei Eish (Y.D. 117) that such prohibition is not mentioned anywhere as opposed to the similar proscription not to inter a tzadik next to a rosho is. He adds that, this is also due to the fact that the kevarim are clearly separated. See also Even Yaakov (28), Harei Besomim (221).
Horav Shlomo Miller’s Shlit’a opinion is that in that in many cemeteries or at least in some sections of them, the common minhag is to bury non related men and women next to each other. If the two kevarim on this question are in one of those sections, he can be buried next to the woman he was once married to.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a