At least some researchers believe that hayfever is contagious.
Only last week, however, I found this advertisement in Science (April 18, 1890) – so this is not a very new concept. (there is an old saying that obsolete theories only die with their proponents, ;-).
More seriously: Reasons for co-disease in your partner can be partner selection by common trait (e.g. in the waiting room of your MD), identical environmental exposure during lifetime as well as many common traits (eating, sport, drugs, etc.).
You may want to check G Bodenmann et al. in Journal of Divorce and Marriage 2009; TA Falba in Health Service Research 2008; GG Hornish in Happauge 2008; D Meyler in Social Science Medicine 2007 as well as AC Eklund 2000 for polymorphisms in the HLA-linked olfactory receptor genes.