The following quote is taken from a letter that Russell wrote in 1960 in response to a fan inquiring about the philosopher’s views on sex. It can be found, as can much of his personal correspondence, in the (highly recommended) book Dear Bertrand Russell.
“Sex is a need and does not require intense love for its gratification. Attraction is sufficient if contraception is understood and used. Love is more rare, but will occur in time. Abstinence only provides inexperience and later difficulty.”