Let's see, her husband stuck his junk in you, did your husband get to stick his junk in her.  Not thinking he did because you stopped everything at that point.  Technically, you cheated on your husband with a man and a woman and he had to watch.  Deal with it, you screwed up and now you are making it out to be that he was the problem.  Looks like you were the problem from the start and are now trying to blame the problem on him.  Get help fast or your marriage is over.

It all comes down to spousal consent, which is so important in cases like this. You were wronged. Period. Don't listen to these people saying you opened doors yada yada.

When the almost foursome happened, it happened with consenting spouses. (What I find dubious is her husband just deciding to stick it in you without consent (?) that's rape (?)) (Foursomes are supposed to be discussed properly in advance - trust me the regrets are astronomical if they aren't well planned)

I don't think people should hold you kissing your friend against you, clearly the men were all for it. It would have been a different matter if your husband had expressed anger at your behaviour. (Was this discussed?)

Back to the topic, let's be clear on one thing when your spouse decides to go fuck any woman without your consent - it's cheating and it's cruel.

You don't have to forgive him for shit and you should tell your friend to go take a fucking hike.

The situation here is much murkier than it would be if this hadn't happened. I think once the door to as opened, you have to just accept whatever happened as a consequence of the initial situation. You had no problems going for it to try to get what you wanted. I think your hubby was entitled to try to do the same thing.