You need to heed the advice on here and put all your energies into cutting contact. I am pretty certain there is not going to be much laughing going on the home of your MM and his DW, I am guessing there is huge distress and pain there.
There is nothing to be gained by contacting her and outlining how deceitful her DH has been towards her, I am sure she has a pretty good idea what has been happening. If she chooses to believe his version of events for now, that is OK. It is for them to sort out. They are doubtless both going into desperate self-preservation overdrive at the moment; by pushing all the blame of the affair onto you will help them both deny his sexuality and infidelity.
Your exBF has a whole load of stuff to work through, both wrt his sexual orientation, and his marriage. At this point in time, there is no hope of a relationship between the two of you. You need to walk away, and let them sort out this mess between them.
I totally get that you are immensely hurt and angry, but now is the time to act with dignity and walk away. Contacting her is an act of revenge that will do nothing but cause more pain to all parties.
You need to get some distance. Other posters have made suggestions how to do this, but blocking all means of communication would be a good start. It doesn't sound like he has done with you yet, and the onus is on you to be the adult here and walk away. This man is a mess - he clearly has major issues with his orientation but isn't ready to address these issues and wants to hang onto his gay lover whilst maintaining the pretense of a happy marriage.
Give them both space and time and concentrate on healing yourself. Access support and friendship IRL, go see a counsellor, keep posting.
Good luck x