Hi @Sosounhappy
you might be right - it could be sexless.
Mine was - because he started shagging OW!
And yes when he was found out he did drop her and scuttle back but the damage was so great, I was devastated. Cheating men who give OW all their time thoughts and passion are very cruel to their wives. Who must just STFU and carry on being nanny housekeeper and secretary.
If you want to know WHY he is splitting his time between boring wife and passionate you - read 'the split self affair' by Emily Brown.
The women are not the problem, something within the man (duty/feeling) is.
The only thing I want to warn you about is that you are wasting your time on someone who is literally UNAVAILABLE. Whatever he says to you, he is not available. Years even decades of your life can go by, don't you want a man and children of your own?
Don't do this to yourself. Either tell the wife (which will end it), or end it and block.