To get separate analytics for the same destination for multiple channels, you need to have unique UTM parameters for each channel. You can add UTM parameters to the long links and then add them individually to your campaign, or you can have them generated automatically by using the channels feature.
There are two ways to do this in Bitly. Using the bulk import template, you can add the same link multiple times, as long as you have a unique channel for each entry. Or, add a single link to the campaign, select Auto-add UTM parameters, and select the appropriate channels.
Each channel will be added as the utm_source parameter, "bitly" will be added as utm_medium, and the Campaign name in Bitly will be added as utm_campaign.
Visit Can I use the same link in multiple channels? for detailed instructions.