Hey jaxmatthew,
We'd be happy to help out. There's no possible way to merge two accounts, however you could always discontinue use of the iCloud.com account, since none of your purchases are associated with it, and then set up a new @icloud.com email that's associated with the Apple ID using your Gmail.com email address.
Keep in mind, the new @icloud.com email must be different than the other Apple ID address.
For help creating an email alias on your Gmail.com Apple ID, check out these steps:
Create an email alias
1. In Mail on iCloud.com, click at the top of the Mailboxes list, then choose Preferences.
2. Click Accounts, then click “Add an alias.”
3. Provide the requested information:
• Alias: The text you provide becomes the email address (alias@icloud.com). An alias must contain between 3 and 20 characters.
• Full Name: The name you provide appears in the From field of the messages you send.
• Label: Aliases are listed alphabetically by label.
4. Click Add, then click Done.
All this info and more is available here: Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support
We hope this helps out.
Take care!