My dad's grief is suffocating over a year after my mum passed


My mum passed from late stage aggressive cancer in September 2018. It's been a tough year and a bit, but I'm slowly getting back to my old self. I'm travelling, enjoying uni and expanding my horizons - as my mum would have wanted. A huge part of why I chose to go on exchange to the US was to get some space from the bad memories and as much as I'm ashamed to say it, my dad. Every conversation I have with him turns into one about my mum. He's constantly emotional around me and tears up almost every conversation. I respect that grief can last a lifetime but it's ruining my relationship with him. I feel as though I can't talk to him because my mood will be brought down and I won't be able to remember the happy memories of my mum. I don't know what to do. Has anyone else had this experience?