Relationship after bereavement....advice please?

my fiancee died nearly 3 years ago and i met someone the other week who i am seeing...nothing serious has happened just a kiss but why do i feel like i am cheating..i feel so guilty when i think of my fiancee....i am 35 and know she would want me to meet someone else....maybe i am not ready for a relationship if i feel this bad.....any advice on this would be great