My partner isn't himself (detached)
Your partner is so fortunate to have you in his life. It's amazing just how many people in our life can leave us 'vibing low', without feeling the need to make a difference. You are definitely a gift to him.
Can you sense why he's emotionally numb? Has it been an emotionally exhausting year for him? Even more intense, has it been an emotionally exhausting life for him, so far? It can be so hard to feel anything when there's just nothing left in the tank. Does he need a difference but he doesn't know what that difference actually is?
We're fascinating, in the way we tick mentally, biologically and naturally. Myself, I'm a mind/body/spirit gal, acknowledging all 3 aspects of self, for good reason. Will give you a bit of a scenario so you can get where I'm coming from:
Imagine your partner is basically emotionally exhausted and feels very little in the way of emotional energy. So, you decide to set the scene for an all over massage. Seeing we feel through our senses, visually you dim the lights to 'peace and comfort' setting, you play music to listen to based on what emotion you wish to generate (either energetic or peaceful music), you burn some oil, based on the scent which smells peaceful. Personally, I love frankincense. Then the massage begins. As you slowly work from the feet up, ask him to quietly take note of any sensations he feels. If you're massaging his feet, he may feel twinges in his back. If you're massaging his calves he might begin to yawn and feel the overall sensation known as 'peace'. So, he begins looking for what stands out in regard to what and how he feels. There might only be little difference yet little difference is a good start, compared to no difference at all.
While all this sounds like a basic natural therapy, there's more to it. An intimate massage can promote more oxytocin (that bonding hormone). It can help generate more dopamine (the chemistry involved in 'pay off'), more serotonin (for happiness or a sense of peace). The list goes on regarding the biological effects. Mentally, you're also creating a shift. Shifting focus from stressful thoughts to peaceful ones or ones of observation in the moment (sensing what he feels) can also help shift chemistry.
If he refuses to consider more complex forms of therapy like talk therapy with a professional or chemical therapy through medication, massage therapy may be a a good start. If he starts asking for more massages, you know you're gradually making a difference.
I am sorry to hear of your situation and how you are feeling. Let's take his health issues out of the equation and focus on how you can feel happier.
If he really has a health issue, he should be seeing a doctor otherwise, please speak to a health professional/clinician for yourself because you do not deserve to be treated the way you feel for your partners difficulties - if that makes sense.
You sound very supportive, so you have done your job in providing care and support for you SO, if they continue their bad behaviour, then I would look at what other options to look after you.
If you partner pushes you back - this is a control tactic and you need to tell your partner clearly that you have boundaries that need to be met.