Really shitty timing, and I'm sorry about the cancer/chemo. It's not too late to break things off with the cheating bastard, though. Unfortunately the "having kids" ship has sailed. And seriously, where do all these shitbags of siblings come from that would knowingly sleep with their siblings spouse/fiancé?

Really terrible timing! I went through Chemotherapy myself - I survived and am in remission but it was a very difficult time. But different people have different experiences with chemotherapy… You are going to need a strong support and care structure. I hope you have family or good friends who can help you. I cannot tell from the posting if the “thing” between your sister and fiancé is strictly in the past or if it is ongoing. Chemotherapy can be hard on the patient and the caregiver in the best of situations. But cancer is no longer a death sentence. People do survive. I wish you well, I hope things ultimately work out for the best.

Who ever said you deserve should rot in hell &I’m so sorry :(

You deserve better.

Both he and your sister are horrible people.