I noticed in your first post where you mentioned that your girlfriend doesn't have sex as a #1 priority. This is completely normal for a person who's relationship isn't based on sex..
For a good sex life to continue in a long term relationship, you have to have other things as a higher priority. Eg, love, respect, good conversation, having fun together, being fulfilled as in individual, work-life balance etc etc. Get those in place and a good sex life will follow.
In the meantime, if sex is #1 priority to you, it would explain why you're not getting any.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.