past relationship guilt

Notes: A = ex, N = girlfriend What should i do? I've been having a relationship for nearly two years, my now girlfriend N is a caring person and i really enjoyed my relationship with her. But before i was with N, i was in a relationship with A but i just feel really lonely when I'm with her, mainly because what we like to talk about is completely different. Our relationship got worse because i was immature, i didn't want to fix what A didn't like about me and instead blame her for not accepting me as is. So when N came into my life i use her as an escape route since i have a feeling she wouldn't make me so lonely. However, 2 years later, i suddenly got haunted by the guilt that i did something wrong to A, i've been thinking about what if i wasn't that immature before, would it be different since A actually cares about me even when i'm that stubborn and reckless. Even though i know it isn't the right choice, i still wonder if i should contact A and apologise for everything