But there's good news, too...
You might have thought it would take five or ten or fifteen years to get bored of sex with your partner - but a new study shows that actually, sexual satisfaction in relationships peaks at just 12 months.
Ludwig Maximilian University, in Munich, questioned 3,000 people aged between 25 and 41, asking them on several occasions to rank their sex lives.
The results were then analysed - and found that people were happiest about their sex life after a year into their relationship.
And contrary to popular belief, the study found that having children doesn't have a noticeable effect of the quality of a couple's sex life.
'We did not find that having children played a major role in a couple’s sexual satisfaction,' said the study's lead author Claudia Schmiedeberg. She added that this is 'remarkable' as research has shown that 'sexual frequency is heavily influenced by the existence and age of children'.
Rather than children, decreases in sexual activity were put down to arguments, with couples saying that more rowing led to less sex.
So you know what to do, folks - have as many babies as you like, but if you want a great sex life, try to put the fights on hold.
Do you agree that arguing is more to blame for a lack of sex than having children? And do you feel sexual satisfaction really does peak after a year? Let us know @marieclaireuk
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