Some things you should have discussed before ever beginning these threesomes: If the condom fails, and she became pregnant, what will you do? Would she take the morning after pill? If she had the child, does she expect financial or emotional investment from your husband in their child? What would that do to your marriage? Why isn't she on birth control now as a precaution? If your husband forgot, where were you? It's not a threesome if you aren't there, and apparently your friend forgot too. If you're cool with the two of them having sex without you, that's fine. But you three should still discuss how safe sex is even more important when there's one less person to remember the condom. I know all that talking may kill the mood, but better a little buzzkill beforehand than all this panic now. As to what to do now, she has to at least take a pregnancy test to even know if she's pregnant, there's no need to freak out until then. And if it's been less than 72 hours, Plan B is still an option. But this was an obvious risk, even with perfect ground rules and planning. If she's not pregnant, you three need to rework the rules of your relationship. Oh, and it's not your fault. It's his and her fault, and your fault (although maybe a little less your fault than theirs.)