I'm a new member too. I can tell things are chaotic for you. There's so much happening to you right now with the illness with your family members and friend. I worked as a therapist until I became quite depressed. I'm not putting that hat on, just responding to your pain.
First, you are not crazy! Life is complex and it's often hard to know what to do. Let me see if I understand what you're saying. Part of you wants your marriage to work, but part of you says you're not ready and at present can't give him what he wants (needs) from you. You also feel you are 'in love' with another man.
I know it's easy for me to sit back and write this, but you have strive to get clarity about your feelings and priorities . If you're not ready to try regarding your husband, you do no good by not telling him this.
There is much in your life unknown so I'm not going to get into advice giving, but you need to take care of yourself.
You're wrting to this site tells me you want to get the feelings out deal with them and have someone else know your pain.
That's a good start. Often writing things out helps with clarity and a stranger(s) can read and hopefully be objective and supportive.
I just want you to know that there is nothing wrong with you as a person, you are not carzy, mad or bad. It might help if you can get more out about what's happening. Have you sought any 'professional' care and discussed your situation with anyone? Also, you didn't mention if you were taking medication or not for the depression.
I want you to know that you have been heard. Also, I know you're not optimistic at the moment. Today is not a depressing day for me, but when the gloom settles over me I can't think in optimistic ways.
Today is my first day here too. Welcome. Hopefully it will be a helpful experience for both of us and others on this site.