Thank you for sharing something so personal. Sounds like the passion or interest is still there. However, the physical expression is perhaps difficult or limited because of health concerns, which is understandable. However, I think your partner is likely understanding of your feelings and probably recognizes or appreciates the other ways you show you care and want her. I think if you let your partner know in other ways besides the physical, that they are loved, wanted, and needed, they will be more understanding if their SO is unable to express it physically.
My question about passion maybe has to do with how intense it has to be, in order for a relationship to continue in a way that makes both people continue to have the same desire for the person. Does someone need a strong desire for the person to continue wanting to be with them? That's another query. At some point, acceptance, commitment, and contentment seem to be necessary traits, maybe more so than passion.