You're gonna have to regain her confidence in you
How can you text other girls and expect your girlfriend to not think something fishy is going on? If those girls aren't your family or childhood friends then you def got some explaining to do.
Next time just stay faithful your girlfriend, you may not have been doing anything but sometimes as women we'd believe otherwise in this situation unless, for me at least, as previously stated above that these women are of some level of importance to you (blood or childhood connection).