caught myself thinking about my last gf

I would like to preface this by saying i hate cheaters. There scum.

My last gf passed after complications from an accident. And we were really close. It's 2 years later and i found myself missing her a great deal and its somewhat affected my overall mood. My current Gf wants to support me but I don't wanna say "i miss my previous gf" in case it makes her upset or not good enough. She seems really concerned and saying I'm fine isn't good enough to reassure her.

I'll get over it in a bit of time but how can i explain it to her?