Oh, Morte, I'm really sorry about this news. I hope it turns out to be nothing, but if it's not, I also think you may feel about it the way you want. I mean, even if you had moved on with a new partner by now, you are still allowed to care for your partner of many years and the father of your children.
And I also think that he turned to you when he had a big problem, because you are still the one he can count on. Of course, he may also be seeking a nurse/therapist/mummy/shoulder to lean on/and lots more, but in the middle of all that, I believe is a window where he knows you are real.
There are examples on the forum of MLCers who did get very sick, came back crying to the LBS, got nursed back to health, and the minute they were healthy again, ran back to an OW. He is still in Replay and still behaving like a child. However, it doesn't mean you can't have your feelings of sadness and fear about what he might be facing. Hugs xxx