Guilt is why. People help people, then people grow apart, it’s sounds fairly normal. You could argue that they failed to communicate with you when you were going through your tough times but then ask yourself if you’ve suspected others of going through the same and if you’ve sufficiently reached out to them. You’re memories connect you to the past so it’s natural you’re brain will cycle over them and if you don’t have a large friends group it’s likely you’re need for human connection will bring you back frequently. Point is you don’t need to go back to ease your guilt, you can help others in the same way as the people who helped you. Build new connections, move forward and if the feeling stays as strong you will have your answer.