I'm so very sorry. To be cheated on by a beloved partner of 20 years, and with a friend too, is devastating.

Open marriages and threesomes are options for some couples, but those approaches come from a place of mutual interest and love.

Your husband's suggestion that you ignore his cheating and join in is disrespectful on a simply stunning scale. As you don't mention even the hint of an apology, it suggests contempt. He has no interest in your feelings.

While I understand you talked to the woman he is cheating on you with, I don't think it's very helpful. It's your husband who is cheating. Even if she were to vanish, it's likely he would simply move on to another person.

I say this because of the lack of remorse he's shown. Normally, people who commit adultery feel guilty. They suddenly realise what's at stake, remember how much they love their partner, and work very hard to repair their relationship. It can be done!

In this case, I don't think that possibility is there. He's confirmed that he is happy to cheat on you, is determined to cheat on you, and so that behaviour will continue. I'm so very sorry to be this blunt, but I think you need to assess where you stand.

You can stay, and nothing will change. You can leave right now, and make your own way. There's also a middle path. That means staying for now while consulting a lawyer to see what your options are and then planning an exit that suits you.

Your kids are 18 and 16, so they will be impacted no matter what you do. If you stay, you teach them that accepting mistreatment is OK.

Also, as you point out, the atmosphere in your home is taxing. If you rush out, though, there may be consequences. These may include them losing their home, there being a custody suit for the younger one, or interfering with the older one's college or job training.

Therefore, I suggest you consult a lawyer. Bring along your bank statements, a list of your assets, joint and held singly, and a statement of your various revenue streams. When you have legal advice, work out your finances.

Once you know your options, pick the strategy that suits you and your kids best.

Again, normally I would advise transparency and honesty as you will be parenting your kids together whether you stay married, separate or divorce. But as your husband has proven himself to be without a shred of integrity, I strongly suggest you tell nobody. Just make a plan, and follow it through.

Once you have your plan in place, you'll need to map out a support network. This will divide friends and family: I suggest you be ruthless and cut out anyone who suggests that you take the blame for your husband's action! Surround yourself with allies.

Also, as your feelings are understandably hurt, and your world has changed drastically, it would help to consult a mental health professional. Not a couples counsellor, but someone who is there for you, and you only. Because at this time, you need someone who is entirely on your side.

None of this will be easy, but I hope this provides you with some ideas about how to go about helping yourself out of this awful present and towards a better future. Please know that I'll be thinking of you.