I would suggest doing your own thing and finding your own partners. Assuming that whomever you are with will want threesomes is a bit far fetched. Sure these things happen and sure it might still happen, but expecting it is kind of a turn off for most women.
I would drop the unicorn idea for now and seek your own partner while he seeks his. It is possible for married men to find women to date if they have the right attitude; not needy but fun and friendly, not assuming sex, but taking time and letting the "relationship" aspect unfold. Other than that maybe you should stick to swinging for him to get his needs met.
Check the tags in the search engine for "unicorn," "dating," and anything else that might seem helpful.
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