I have been through this and still am going through this. A lot of the regrets I have in life have happened to me when my bipolar type 2 was still out of control. I've screwed over a lot of people and myself countless times. Now that I am stable (at least the most I have been) I reflect on the past and feel a lot of shame and remorse. However, it's best to not look into the past and only into the present and future. What has helped me is my developed faith and personal relationship with Jesus Christ. I'm not sure if you are religious or not, but it is the best advice I can give you. I have repented for sins and have a much different, better outlook on life. I still feel remorse but being forgiven has helped me a lot. If you are not religious, just staying away from the past can help. Learn to forgive yourself for the past and to only look forward.