Your partner should be your best friend but one should try to have some other friends too. For me that is extremely difficult because I'm very intelligent and have had many life experiences that almost no one will have. Few would understand me.
Finding someone able to be with me who I respect and admire is very, very difficult. I find most people just too ignorant and lacking in knowledge. It's like the other adults around me never grew up.
For me, it has to be my partner that is my best friend... that is why we are partners. But my partner has died so now I just have to cope and I was always reclusive from others anyway. I find my sister a good friend and, while not able to be my best friend, she is someone I appreciate and can express myself to.
So I understand your loss. It's been nearly 17 years for me now and the first 10 were the hardest. I'm too old and not well to expect a new partner, but you may yet find another. I like to think there is a reason these things happen. My partner who died wasn't the first in my life but definitely the love of my life.