This situation would put me in a quandary. If I'd already decided to leave and my partner was diagnosed with an illness...a bad one....I would have to take into consideration years ago when I was in hospital, 39kg at 27 yrs, losing weight but needing an operation. My partner came (walked! we had no car) to see me every day. And when I was ill he was always there for me. He was only 19 but looked  after my children too. That early concern for me, the care and responsibilities he took on..may make me see the situation differently. While our relationship has changed beyond all recognition....there is a part of me that could still, I think, put his health and well-being first, though it would be a very arms-length and sterile support. I am a mother, my first thought would be to nurture...or help with finding others who could

Such an personal and individual decision, with circumstances and boundaries that only you yourself will experience.


 

If you do not want to continue to be his wife I have a couple of thoughts which may sound cold and crass. If he is seriously ill his medical expenses could leave you in an even worse financial situation and you may want to consult an attorney now about what you can do to keep some money for you to live on.

Also if his illness is terminal would you be better to wait? I knew of a woman who wanted a divorce ASAP when she found out about her husband's mistress. When she learned that he had an inoperable brain tumor however she told her attorney to stop everything. He might have wanted to marry his mistress but she knew that it would take him longer to divorce her than he had left.

You don't have to be as spiteful as she was and can help him during his illness to the extent you want to but don't ignore your well-being because of him.
 

Mimi wrote:

Update to my situation. After I confronted him about knowing about the gay hookup sites and many ads, he claims that he’s never been physically involved. He’ says it’s only curiosity. Tells me that it’s both of us contributing to where we are in our marriage. Had I been more affectionate he wouldn’t be “curious” about men. (Yup he said it).
Wants me to see couple’s therapy with him so we can “solve” our situation. I think he wants me to forget what I saw, and accept what he tells me as facts. Love bomb me with fake promises of a better marriage which can never happen. I can’t undo what I know. It’s only moving forward from this point. It’s not my fault where I am right now but it’s my responsibility to do something about it!

This sounds so familiar. "It's just a curiosity" is my GIDH's mantra at this point. He does not ever blame me for his curiosity or shortcomings thankfully but he seems to think therapy will just bring us back to loving partners. 

You are so right when you say it's not your fault but it is your responsibility. That's exactly how I feel. My husband isn't sick but I still have moments of doubt and guilt that I'm abandoning him. He won't be truly alone because he has our children and I've even been stepping away from our mutual friends so he can keep them. I will miss them but I need my own life away from my husband.