Husband sleeping with lesbians

When my husband and I first started dating he told me he was helping his married lesbian friends conceive a child by donating his sperm. He said he never slept with them but would do his thing in a cup, they would take his sperm and use a syringe to insert the baby batch inside of her. I told him I didn’t want to date someone who was essentially gong to have a baby even though it wouldn’t be “his” I wouldn’t want to be in the middle of that so he stopped donating his sperm. Fast forward 3.5 years, we are married and have a 3 month old son. The lesbian couple, myself and my husband have remained close friends and they have a child of their own. Well a friend of ours slipped up telling me that “it wasn’t always done in a cup.” I was so shocked that my husband had lied to me about this! I asked him and he denied it at first, then confessed that it was true. Even though this happened before we were together, how could he lie to me about this?! I feel so stupid becoming great friends with these lesbians that have had a threesome with my husband and that my husband lied to me about it.