I agree with what Fellatio said.
I don't think couples counselling would be productive, especially as the counsellor was surprised by the things you have told her, given that your H also goes to her and should be honest with her. Your H clearly has a good deal invested in his lie and you will not manage to crack him in counselling.
My exH threatened suicide when it became clear that I was not interested in wasting my time with any more counselling. He spent time in a psych ward - long enough to be diagnosed with major depression and to get a prescription for ADs which he stopped taking after a few weeks (he had a notion that mental illness was a weakness that could be overcome by force of will -- maybe he thought being gay was similar). His mother (whom I hate, I will bluntly admit) told me there was nothing amiss medically speaking with her son but a 'bad marriage'. 
So all my fault then.... In the end I agreed to go to a weekend couples retreat and a course of workshops that ensued, basically so that I could say I had done everything anyone (mainly exMIL, who was pressuring both exH and myself relentlessly) could possibly ask of me to keep the marriage alive. It was about two weeks after exH had written the cheque to pay for the retreat that I found the gay porn.
It may seem heartless, but I found the suicide threat a very alienating experience and was conscious of an element of manipulation to it.
We went through the motions of the retreat and all of the workshop sessions, with me hoping he would reveal it all to me, but he never opened his mouth. It was clear to me that he thought his secret was well hidden, and also clear to me that he only meant to answer questions as I asked them, and even then I was likely to get a shrug or an answer that contradicted a previous question along the same lines -- he wasn't going to volunteer any information. Trust was out the window. I knew what I had found but I didn't know what else there might have been and I knew he wasn't going to tell me anything I didn't already know.
Just telling you all this as an indication of how closely a secret can be guarded even when the issue of trust is known to be a massive one, and one capable of breaking up a marriage just as much or maybe even more than the matter of being gay might.
Investigate what tax and childcare benefits are available to you in case of separation -- go to the CAB. Try to keep working if at all possible. It is hard to get back to work after being away and the late 30s/early 40s are a witching hour of sorts where the workplace is concerned, for both men and women.
Ideal scenario is that you would manage to agree to an amicable split where he could be persuaded that he owed you sufficient support to afford childcare and to stay working (but look at CAB too). Or that he would support you through further education or training that would lead to a better-paying job for you (maybe in lieu of some financial support from him after you get that better job, or in lieu of sharing his pension, or trading off the prospect of you getting 60% of the proceeds of selling your house, getting a 50/50 split instead )...