Substitutes are indeed everywhere:
This paper examines the association between television ownership and coital frequency using data from nearly 4 million individuals in national household surveys in 80 countries from 5 continents. The results suggest that while television may not kill your sex life, it is associated with some sex life morbidity. Under our most conservative estimate, we find that television ownership is associated with approximately a 6% reduction in the likelihood of having had sex in the past week, consistent with a small degree of substitutability between television viewing and sexual activity. Household wealth and reproductive health knowledge do not appear to be driving this association.
That is from a new NBER paper by Adrienne Lucas and Nicholas Wilson.