The first thing that jumps out of your post is that there are so many positive things there, lovely granddaughters, supportive partner, brilliant with them, helps with childcare. It could be so much worse, so just maybe try to 'count your blessings' instead of focusing on the bad things. We all have that choice and I know it can be hard, but switching to a more positive outlook will change your life.
The same applies to your partner. Despite his good points you still say you sometimes hate him, but I always tell myself that no-one is perfect, we all have bad points.
Remember this is the worst and most depressing time of year, but think of Spring and longer days being just round the corner. I hope you can shake off those bad vibes and get into a more positive head space. Maybe a book or website can help as there will be many I'm sure.