I feel really bad about it?

Well it depends whether or not you still have feelings for Cody. If not, hopefully not, you should tell Morgan that you really don't have feelings for him anymore and that past is past. It should reassure her a bit. Maybe don't spend too much time with him too. And if you do, invite Morgan. She might not like you but I bet she likes the fact of you and Cody hanging out alone even less. Good luck! Let fate lead the rest!