Well technically it’s the food, but your spouse is making you so comfortable in your relationship that you’re eating all that food. According to a study by British diet company Forzadie, couples gain an average of 14 pounds in their first seven years together and then four pounds per year.
It makes sense, when you’re single you make a point of looking good, keeping active etc., and in a relationship you become more sedentary, perhaps eating in and watching movies on the couch.
That being said research has also shown the couples that gain weight together can lose it together. The survey found that more than half of the couples had tried to lose weight together and most believed it was easier to lose the weight as a couple than alone.