You appear to share common interests and possess a similar outlook. A pattern emerges. One night, lying there in the afterglow of another good session, you tentatively ask what the score is. Every time these thoughts creep in, you remind yourself of when you were laughing a few weeks ago. You remember the stuff they talked about doing with you but have made no moves toor when they said that they really enjoy your company. After posing the question, the atmosphere changes. They pull themselves onto their side and look at you.
The majority of lessons we learn a propos monogamous relationships are only about the joyful beginning, and not the act that comes after. That sounds improper to some people; disrespectful of your commitment to your partner. But accomplish you know what that imagining does? It gives you an opportunity en route for make a choice — to adjourn or to go. And by allowing yourself to imagine a different actuality, to acknowledge the possibility that you could conceivably be with someone also, and to still choose your partner? Not idealised, not ignorant, not adolescent defaulting; but conscious, chosen, ongoing allegiance. Noticing what is appealing about these fantasies can illuminate feelings or desires that are currently unfulfilled.