Gomez is said to have flown boyband Union J to one of her shows in Portugal and spent a night with Shelley, causing him to miss his flight back home.
The 21-year-old singer also hosted a private party at her Lisbon hotel suite and invited Union J members as well as her crew, reported Aceshowbiz.
"She invited all the Union J boys and some other members of her entourage to her room and they had a great time drinking and dancing. Selena and George were all over each other and things got very heated.