Hi Jeremiah,
You could add a dropdown to your Opportunity table for "Realtor", choosing the Contacts table as the list of values for the dropdown and RecordID as the value to display. You'd also want to add a Linked Field for the Contact's (Realtor's) Name, linking it through the dropdown you just created. This will allow you to select the Name field for the list of values when you place the dropdown on your screen, instead of the RecordID field.
You could then add the dropdown to your Opportunity screens, filtering it to only show Contacts where their Campaign = YourRealtorCampaign (or Contact Type = Realtor, if you have something like that set up). This will allow you to associate a Realtor with each Opportunity, at which point you would be able to run reports or build a grid to list all the Opportunities a Realtor has given you.
Hope this helps.
- Justin