Something similar for us. After breaking up with my ex-fiance Red while continuing to have sex with him, I met the man who would become my husband and started fucking him too. Both were good with it and both men were monogamous with me. Red, however, made a point of saying that he would always be faithful to me; not that I insisted on it, but whatever.
After a while I got hubby hooked up with several women, which opened me up to my Lesbian side, but Red stayed committed to monogamy with me (I flattered myself that I was meeting all of his sexual needs, which probably was true). One of the women, Clair, joined us and we felt like a family, not just a married woman with a bf. Clair got unexpectedly pregnant (by hubby) so I followed (going "potluck" with the two guys) and having children made us feel like a real family. We started swinging with Lora and her boyfriend (who became her husband), but Red was still monogamous with me. It wasn't until some time after Lora left her husband, moved in with us and joined our family and we had our second round of children together that Red gave up his fidelity and started having sex with Lora and Clair.
Funny how men are and that all was, but it's worked out.