@marama,
After a decade long relationship, it is normal to have a strong emotional connection with a person. It is also normal to grow apart from someone. Is there some co-dependency occuring between you? Perhaps he is used to you always being there for him as the strong and available partner, but perhaps now that your emotional energy is going towards a loved one who needs you, he might be missing your strength like a crutch. Also, the push and pull in a relationship can get hard when you are trying to climb a ladder and someone keeps pulling you down to their rung. I recommend watching some Youtube videos on co-dependency and how to overcome it.
That being said, requiring your partner to be there for you when you need them requires vulnerability. In order for him to provide support, he has to understand that you are not always going to keep it together, especially when major life changes occur. You need someone there for you too and, at the end of the day, you must do what you feel is right for yourself.
Perhaps the best option in your situation, considering the emotional energy you have put in, is to tell him you require a break from the relationship for 2 months. This gives both of you a boundary of time to adhere to, and will give you some initial space to assess your feelings during this trying and changing time in your life.
You have established that after 10years he is incapable of providing you with the support you expect from a partner, so in those couple of months you can consider what other avenues of support you could create for yourself and your parent. Tell him your reasons for needing a break, perhaps let him know you need the time to seek out support groups for yourself or seek support from family members, or even that you are having your own emotional break. If he understands that you are in need of support, he will either rise to the occassion or not; and honey, if he doesn't, then walking away may be hard, but it is the right decision.
If he contacts you after 2 months, you can assess if he is stepping up to meet your standards of a partner. If he is not, then you can go ahead and make your decision from a clearer perspective of whether to promote or fire him.
Good luck and all the best.