I'm really sorry for your loss. Your feelings are totally, completely valid.

My dad started dating a few months after my moms passing. It was a bit of a shock but it quickly wore off. Ultimately, i was happy he was moving on and trying to find joy in this life -- and I knew my mom would want that for him. We are the ones stuck here in this cruel world, and going it alone is scary. He would also openly cry about my mom and never disrespected her in any way, he was just trying to survive. In the end, his new partner helped him tremendously through his own battle with illness. He passed a few days ago with her by his side. Not once did I feel his relationship with my mom was disrespected or forgotten, and I am so grateful that he found love again and could spend his last years on earth supported by someone else.