Marriage, to me, is a partnership. I knew of a story of someone who slept in different beds during the height of menopause but that's just something they needed to do after knowing each other since their teens. But they still made plans despite the day to day doldrums.
Maybe tell husband #3, that traveling is a serious need and go from there? Boredom can strike anyone. Maybe this call by #2 was a wakeup call?