Is Katie mcgrath girlfriend of colin Morgan?

No. But I could see how some people would think they are. Katie just got married but the way she looked at Colin and was constantly flirting with him was really confusing considering she had a fiance. I don't understand her, if she had a fiance and was about to get married why would she make people believe her and Colin were together by the way she looked at him like she loved him. Confusing.

EDIT to add to original: Because she loves her the way friends love each other. They were all together for five years, with 8 months of filming (12 hours per day). No need to be romantic for friends to love each other. Also, maybe she looked at him as a younger brother since he was the youngest of the cast for a long time, plus is Irish like her (Katie is 3 years older).