I Feel Stupid for Grieving

I feel so stupid that my heart is still broken 5 months later. My 12 year old dog passed away back in May, he was my first dog and literally my best friend. My mom and sister are on a list to get another dog next month, and my sister keeps calling me a “joy suck” for still being sad about everything. How can I become more at peace with losing him? I just feel like I can’t replace him and shouldn’t replace him, at least not now. Every time I talk about him I cry, and even my boyfriend says that if I get another one I’ll be happy. I just feel like I can’t be happy without him.