I'm sorry about your loss. You shouldn't expect to be over this personal tragedy in just one month. People grieve at different rates, but that would be tremendously fast. In high school which was around 35 years ago for me, I lost a friend I adored to suicide and can attest that there are some things you never 100% get over. Your sadness and regret -- I imagine at not telling your friend how deeply you felt -- further complicates your grief. If you can see a counselor (e.g.,psychologist, licensed clinical social worker) it may help you through this period.
Alternatively, you could also talk with an adult in your life who is a good listener and has years of perspective. You may be surprised what some of the adults in your life have been through in their youth. If appropriate, you could also arrange a visit to your friend's family (their mother in particular). Bring flowers or some token to brighten their day, and let the family know how much your friend meant to you, including your regret. Telling them may provide you some consolation. You might even maintain a relationship with the family.
This loss will be difficult to process, but you will get through it. Please lean on those who care about you, and get professional help if you need it. Specifically, if you find that your grief is still heavy after 6-12 months, you may be experiencing complicated grief and suffering from depression, a treatable condition. In that case, you'll need to see a psychologist for help.