If you have no life outside each other and the children, emotionally you can reclassify each other as brother/sister and subconciously awaken the incest taboo, as in the case below:
www.theguardian.com/lifeandstyle/2017/may/08/retired-couple-together-all-the-time-cant-perform-sexually
So even if it feels counter-intuitive, less time together and leading your own lives may help your relationship and sex life. This advice massively helped me and hope it helps someone else!