Hello and welcome.
It's a very difficult and emotionally complex situation. Balancing your long-term marriage and family with the deep feelings you've developed for this other person must be incredibly difficult and challenging. It's clear you care deeply about all the people involved and don't want to hurt anyone.
The added stress of your affair partner's illness likely makes things even more complicated and emotionally fraught. It's natural to feel conflicted and unsure of how to proceed.
I can't advise on the right path forward, as that's a deeply personal decision. It might be helpful to speak with a therapist / counsellor who can provideyou with unbiased support as you navigate this situation to find a way forward.
Please take care of your own emotional wellbeing during this stressful time.
