Traditionally Diamond is the stone for long marriage, but it will enhance and emphasis whatever the emotions are, for good or for bad that is so be careful, but Morganite ( Pink Beryl) can be great for bringing back love to a marriage, Ruby and Emerald for infidelity and for calling back to the partnership. Sapphire for faithfullness and love and stability. The aspects of using gems as you have asked is more tied into spells and not gemology or crystal healing. At the end of the day, crystals will probably work their ways too slowly and subtlely for there to be any great difference, so I wouldnt rush out and buy any for these problems, my reply is more of a guidance to why these stones are given in engagement rings and wedding rings before the event
