eBay cannot merge your accounts. This is not eBay customer service, it's a discussion forum. We are fellow sellers.
1. Go to the account currently using your primary e-mail and change the e-mail on there. Create a throwaway e-mail if needed for this purpose.
2. Request to close that account. Read about the process here. Or leave the account dormant, or keep it for buying while you use your other account for selling.
3. Now that your primary e-mail address is no longer tied to your old account, you will be able to add the e-mail address to your new account.
If you want to change your ID in the future, just change your eBay username instead of creating a new account.
