Girlfriend's Odd Behavior?

My girlfriend of 7 months is here in NY for 2 years on a work visa from London. She has 2 male roommates. The 3 roommates decided to throw a Xmas party this past weekend and while I was there she introduced me to a boy, who is friends with one of her male roommates. During the introduction she explained that the friend was about to embark on a trip through Europe and that one of his stops was London. So she arranged for him to stay with her closest friend in London for 2 days, wherein she also offered him a place to stay with her parents. In addition, she herself will be traveling back to London for 2 weeks to stay with her family...and since they'd be there at the same time, she was keen on spending time with him there.

She thought there was absolutely nothing wrong with her making these arrangement with this boy while in a committed relationship with me. Am I wrong at all for this to bother me?