I would say go for having more sex with other girls and she doesn't need to know about that. If that's really your problem (needing different and new experiences) then it will be solved after a while. And if it isn't, you would know it and maybe get back to her more stable and assured. But if you don't try it and the thought never stops coming up again and again, how you gonna find out what's really the problem? and how you gonna live with it?