I wonder if it would help for you to slightly shift your focus in trying to find a way through this situation. From what you have stated, at the moment it sounds like you are focusing on how you can get him to change. You want him to understand that from your perspective things are not well, and you expect this to be enough motivation for him to also feel that things are not well.
However from his perspective, there doesn't appear to be any motivation for him to change. Things are exactly as he wants them to be at the moment, and he can clearly live with you not being happy.
What I am trying to say is you cannot change or fix him - only he can do that.
All you can do is change yourself. At the moment you feel as though you are in the role of housekeeper while he has his affairs. If you separate you feel you would have nothing. I take it from this you are not married and so wouldn't have rights in this respect, but perhaps rights as a common law partner. I am not a solicitor, however perhaps seeking legal advice to ascertain your financial rights if you did separate under the circumstances, would give you a better idea of where you would stand if you did leave, due to his infidelity.
On a relationship perspective, only you can decide what you will and will not put up with. We teach others how to treat us. If you have been in this relationship for 35 years, you know what the future looks like if things remain the same. If you know that you cannot change him, and you focus on yourself, what do you want things to look like for you in the future if you stay, and if you leave.
What needs to change for you to get to where you want to be, what do you need to do to make that happen. You do have options, you could leave, and start again. You might have nothing materially, but you would have control over your life, and you may be happier.
If that doesn't feel right, consider if you stay, what do you need to do to make this manageable for you? Maybe change the relationship you have with him, change your focus away from the relationship you have with him, and towards other ways to fulfil yourself and your life, without him, but in the same house. How would it feel if you focused on yourself, did things you enjoy, but without him, increased your contact with other people, gained fulfilment outside of the relationship. Consider whether that would make it more manageable for you?
This would give you the financial stability, but also allow you to gain the fulfilment you desire from a relationship - it doesn't have to be with him.