HELP.. do I do it or not?

Is getting my girlfriend a dildo bigger than my penis a bad idea? Im 5.75 inches long and 4.7 inches in girth. The dildo im looking at is 7inch long and 5.5inch in girth. I want to really bad (I really don't no why) and I have brought it up before while having sex and she gets off almost instantly so I think she really wants it. But Is it a bad idea? Is it gonna drive her to cheat or not enjoy normal sex with me anymore?
HELP.. do I do it or not?
Add Opinion