Then it really sounds like this is a red herring, OP. And if your DH and his mother are that close, to be constantly spending time together, more than he spends with you, then it’s possible she didn’t come to the hospital because she was in denial about what was happening and he completely accepts that.
I’m not saying this glibly or sarcastically, but you sound like a martyr. You’re sacrificing yourself for everyone, and they’re not supporting you. It’s not fine and lovely that he and MIL do everything together when he’s not working; you’re being cut out of your own marriage. It’s not sweet that he went on a nice picnic with MIL when he won’t make time to go on couples’ activities with you. No wonder you’re so worried about MIL acting coldly to you - she’s in control of your DH, and he’s either fine with it and going along, or actively facilitating it.
When you add in the fact that your life sounds currently depressing (an endless parade of caring for sick relatives, none of whom sound particularly nice about it) and then you say, I need to learn not to confide in him my fears, my worries, my concerns and my grief and absolute loneliness, it all adds up to a not-so-nice picture. No, OP, that’s not something you need to learn. It’s not normal to be unable to share with your spouse.
This thread started about a row you had tonight, but I don’t think it’s about tonight’s row, I don’t think it’s about MIL and the hospital, and it may not even be just about MIL’s treatment of you. It sounds like your DH may have checked out of your marriage, and you deserve more happiness than putting up with that forever. 