Devastated.....It may be very lonely where you are, but you're far from alone. Both here and in life in general. Whether it helps to know that or not, I don't know, but a surprising number of people do the kind of dastardly stuff your husband has done. I don't know why he told you at this point, maybe because you found out about the STD and he just can't lie that away, or maybe he's tired of being this person who sucks....and people who act like him DO suck.....Personally, I'd like to know if I were you, why he confessed at all after lying for so many years.
I understand being with someone a long time, 40 years is a long time. There's a name for this kind of financial concept - sunk costs, I think it's called, where you put so much into something over such a long period of time that you can't imagine leaving because.....you put so much into something for such a long time. But do you REALLY love this guy at this point, and why? Do YOU really want to continue this marriage as a relationship or just as a front because it's convenient, you have a family, a house, a social front, pensions, whatever....that's okay if you do, just understand why you would want to stay. Are you afraid of being alone? Are you afraid of being shamed, that divorce is shame? Is it a religious thing too? All of these things matter but to me, the bottom line is....you should also be willing to consider divorce because your husband has made a lie of your marriage for many years. All the things we expect from marriage he has willingly defiled. Even if you want to stay married and try to heal this, get past it....you should still be able to openly consider divorce because otherwise you become a hostage in a marriage that really isn't a marriage....it's a mirage. Even the serious threat of divorce becomes a lever for change in him.
I don't even know what change in him would entail because....how do you trust a man who has led such an extensive, really in my opinion, degraded life, that has endangered both of you. Physically, emotionally, possibly financially, maybe socially if this had got out. The way he has lived secretly from you is degraded. Can you really accept that this is the man you still want at this point and how would you even assess that kind of change? Can you look at him the same way now as you did?
Don't rush into reconciliation. Consider divorce, I think it's often the best option because I don't know how many marriages can really survive revelations like this AS a real marriage. Yes, maybe because you need a place to live, the kids, the assets, it's familiar, that's all okay as long as you understand that's what it is. But love, trust, affection, respect....those should be part of marriage too, I think the main part of marriage. Realistically I don't know if you can get that back. I would talk to a lawyer to see what divorce would look like for you....you should at least know these things.
As far as counseling it can be really hard to get a good counselor for all the reasons you know. I might suggest on line counseling services, they are available and might help. At least it would give each of you - and you probably should have separate counseling at this point, in my opinion - a sounding board for your feelings and ideas and help you each to clarify how you feel about yourselves, each other and the marriage at this point, and help you determine how to move forward.
I'm so sorry you are going through this, it's a terrible disappointment, crushing I think, to discover that one's spouse is a very different person than we thought. TO me this negates the idea of marriage, but that's just my opinion, it might not work for you, but I want to offer this. ALSO KNOW THAT NONE OF THIS IS YOUR FAULT - THIS IS ALL ON HIM. Just in case that ever comes up and it does come up as a defense surprisingly often. Don't accept that.....this was all his choice. Maybe he can change now, but....do you stil love this person? Only you can decide.