Love takes many forms. Caring for someone without the expectation of a benefit you want is a form of love. If my wife came down with MS and we could no longer have sex, I would still love her, respect her and admire the mother and life partner that she is. I would also be upset that I couldn’t have sex any more.
I personally would try to figure out the following, with or without professional help:
Why is she depressed? She is going through a lot. She is probably scared you are going to abandon her when she needs someone the most. She may also hate the situation that you are in because of her illness. She is also probably angry at the world that she has to suffer this. She is also probably worried for her child and feels guilty that she can’t give her more. There are so many feelings she has to process, it may be easier to just shut down.
If you remove the expectations of sex with her, would you be willing to stay with her as a caring and respectful partner and mother to your child?
You might explore non-monogamy. That’s going to be a complicated conversation, but maybe something your wife is willing to explore. Just ensure it takes into consideration all the issues in the first point.
A good mother and partner is so hard to find. Love can take many forms. Don’t feel limited in your choices if you can make other options work out.