Maybe you need to take a half step and get adjoining rooms at a hotel or rooms in your home. You do a threesome before bed or just let them enjoy themselves. Then in the middle of the night she wakes you with a kiss and goes to visit her lover in another room where you can hear them having sex but you give them privacy. Then she returns to you after their middle of the night love making with a treat for you! Your call whether it is sloppy seconds or cream pie cleaning. Then in the morning you could just let them make love again or let the sex take its own course as to whether you are involved or not ... The hottest would be for you to have to go to work and you leave them in bed together as you depart!