Historically obviously marriage developed to pass on land etc but mistresses were common, then creating economically stability when having children and going back to ancient times a protector for family. For me monogomy is hugely important and my husband is the one person I am attracted to. Scientifically apparently you are more likely to be attracted to someone with immune system that compliments yours for healthy children. I think the fact as humans we feel love for a partner means that we must have predisposition to stay monogomis
I have an awful immune system and OH has a brilliant one, does that mean he should not love me
Actually, she's right. Very interesting studies done on this and how it affects the chemistry of attraction. We can sense pheromones in sweat and are attracted to those whose immune systems best compliment our own. So in your case, his being great and yours being awful (as perceived by you - remember he may only be bringing immunity to colds, etc and you may be bringing immunity to some big bad guys that neither of you knows about - impossible to say without a genetic analysis), means he's filling in the gaps in yours for the best possible outcome for your kids. If you think you have a really bad immune system, however, you need to have a word with your parents!
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