k guys, i have a pretty legit issue that i would appreciate some "expert"

advice on haha.
so, my girlfriend of five years is pretty awesome. i mean, you couldnt ask for more from a girlfriend, she is completely supportive of all my endevors, gets along great with my fam, cooks and cleans out of habit (she is Susie Homemaker herself, i swear), and in general is a goofball. we've had some great times together, which goes without saying because otherwise i wouldnt have stayed with her for so long. but here is my issue....
i started dating this girl my freshman year of college, when i should have been getting all the wild and crazy shit out of my system. I never would have thought that we'd have made it this long when i started out, but i got really attached and so did she. anyway, i dated her all throughout college and now that we've graduated and moved in together, im starting to really feel that maybe ive made a mistake. the problem is, she no longer intellectually stimulates me anymore...we dont have interesting conversations and she has nothing to say to me that i didnt know was going to come out of her mouth before she did. she lives and dies for me, and because of it she has no other friends (doesnt have the best of times with my friends either), has no hobbies of her own, and in general is pretty boring to me now. on top of that, i go to the gym all the time to stay looking good, and she eats twice as much as i do and NEVER makes an attempt to stay in any kind of shape, and thus im not really feeling how she's going to look in a few short years. couple that with the fact that sex is almost routine, and you have me looking for a way out.
now, i LOVE this girl, and i dont want to hurt her, but im just not so sure that i cant do better. i mean, i could do without the cooking and cleaning if it meant i could find someone who could match wits with me every now and then.
guys, the point is, im not sure why im feeling this way, if its normal, or if i already know what i have to do and just dont want to go through with it. if anyone has any experience with this kind of thing it'd be most appreciated to float me some words of wisdom.