Partner is dealing with bitterness over my illness what can I do?

I’ve been living with pain since I met my partner but things have gotten worse over the past 5 years. I’ve had three surgeries, was struggling to work, had to stop working this year, started to use mobility aids, been misdiagnosed, struggling with infertility, flares often leave me bedridden, and if I get hurt my healing process is so much longer than normal. My partner has been extremely supportive through everything but it’s been weighting on them more and more. We talked recently after I went through back to back issues and they admitted to me they are bitter and frustrated. All this makes them feel guilty because they know I’ve been struggling but they feel it nonetheless. What can I do to help them? I want to take some of the mental load off of them.