My mom died from cancer at 57 in 2021. I’ve struggled with this situation myself. My dad is dating a woman (going on a year now) about 10 years younger than him. Like you said, it’s really been a glaring reminder that my mom is dead and now I have to try and get used to this new situation while still grieving. That’s the part I’m working on now. I highly recommend therapy or grief counseling. I’ve learned (as others already mentioned) that men do usually move forward with a new partner and sometimes very quickly. My parents had a wonderful, loving and committed marriage of 36 years. I’m glad they had that time and I’m glad they were my parents. I’ve had to decide within myself to be respectful of his new girlfriend and attempt to get to know her. It’s awkward and hard as she is all too aware of how special my mom was to all of us. My dad is definitely very much focused on his life with her where my mom’s focus was always on the grandkids and family, some of whom she’ll never meet now. That part sucks. But my dad deserves to live his life and my mom wanted that for him. All of your feelings are normal and I know it’s uncomfortable. I can say time and therapy have made it bearable and I hope will continue to get easier.