@mandy5dawn I haven't seen all of Total Drama All-Stars so I had to look up what happened on the wiki of their relationship. Going off of the description of the episodes, I feel like it was a perfectly good reason to dump him. Duncan wanted to see Courtney get jealous and even asked if Courtney had said anything about him after they swapped teams and personally, that would make me wonder if he actually loved me or was just using me to make the other girl (in this case Courtney) jealous so I can understand Gwen ending it, feeling that the romance was gone. I suppose she could have handled that better and tell him how she felt to see if they could work things out, but they're teenagers and don't usually think like that. Although, I can attest to it being incredibly difficult to stay in a relationship where one side isn't feeling the same about the relationship the same way as when it started.
However, if I watch TDAS and actually seeing things play out changes my mind, I'll let you know.