WIBTAH for remarrying my ex even though I’m going to die?

I know this post is morbid and dark, so I apologize for that.

I (36F) am close to dying. I have terminal cancer and I only have about a year or two left. I’ve accepted and made my peace with it, and I don’t mind openly talking about it. I also have a less than common relationship. My current partner/boyfriend (38M) is also my ex-husband.

Me and him married right out of high school, stayed together through college, had three kids together (12M, 11F, and 4M). We divorced when our daughter was 3 because of his intense work schedule. It was a lot of heartbreak and pain, but at the time it felt right for both of us despite that.

Two years after the divorce I was first diagnosed with cancer, and he reduced his work hours so he could take more time with the kids, and it slowly shifted to him also taking care of me, and we rekindled our romance, but didn’t get remarried. I got lucky the first time around and was declared cancer free at 31. I had my youngest child at 32, and was rediagnosed at 34. We tried treatments but it’s been recently declared terminal.

Please don’t feel sorry for me or throw me a pity party. I’ve gotten to live the life I wanted and I’m okay with the fact that I’ll most likely die before 40. The only thing that causes me any emotional pain is that I won’t see my kids grow up and experience life milestones like graduating, getting married, and having kids.

Long backstory, but here’s the problem. My partner and I have discussed it and we want to remarry each other. I want him to be listed as my husband in my obituary, I want him to be able to make medical decisions in case I’m unable to (this one is big for me because of my situation), and so that he can get Survivor Benefits when I pass.

My sister (38F) says that it’s cruel to remarry him knowing I’m going to die soon, and that if I loved him I wouldn’t have divorced him in the first place and that by remarrying him I’m disrespecting the sanctity of marriage by doing it “willy nilly”. She also said I probably used my diagnosis the first time around to get his pity love so he’d get back with me since it resolved the main issue from our divorce.

So, Reddit, I was wondering if it’s really bad for me to remarry my ex? I love this man, we both regretted our divorce and are so grateful that life brought us back together, but now that I’m close to death we want our love to be legally recognized.