ValidatedProgrammingand Styling
Hazan, C., & Zeifman, D. (1994). Sex and the psychological tether. In K. Bartholomew & D. Perlman, Advances in Personal Relationships (Volume 5). pp. 17-52. London: Jessica Kingsley.
Found that it typically takes around 2 years for an adult romantic relationship to take on all the characteristics of attachment relationships.