I think what many posters are missing here is that this affair has been constructed purely with the aim of giving the Op and her lover a sex life.
It's not about falling in love, or an emotional connection- it's about sex.
If faithfulnesss boils down to not having sex with anyone else, then she is unfaithful. On the other hand she is staying in her family to try, I assume, to protect everyone from the impact of a divorce.
Yes, there is deception, but her DH has a choice doesn't he? He has a choice whether to stay in a sexless marriage or not. He has a choice to stay with a wife who may find sex elsewhere. More importantly he has a choice to try to rectify his marriage- and he hasn't.
The "blame" here lies not solely with the OP.
OP- if you can continue this affair discreetly, and maybe it's too late for that, and if your DH can turn a blind eye or never know, and if you can pretty much guarantee that you won't fall for your lover and try to break up his marriage, then carry on.
If, on the other hand you fall for him, he falls for you, or whatever, then that changes things.
I think you have to tell us if this is an emotional connection, or just sex.
OP- if you have honestly tried to persuade your DH to have counselling, medical help or whatever it is that he needs- or maybe he simply doesn't fancy you anymore- and it is not working, then I think you should grab what happiness you can.
However, if you have not really tried, or your marriage is over in other ways, you need to address that first and not simply paper over the cracks by finding a lover.