Okay, so I've been with my girl for nearly 5 years (will be 5 years in December). I feel like my heart's not really been in it for the last 8-9 months, and it's been a long time since I was properly sexually attracted to her (probably a few years). In the last 3-4 months I've started to notice other girls and develop crushes on others (not friends though). I'm going through a lot of conflicting feelings and the upshot is that I think that it's probably best we break up, but it feels like there's so many complications.
I've never broken up with anyone myself (though was broken up with by another 5-year GF) and so it feels like such a big deal. I still love her but not in love with her, so obviously don't want to hurt her (but obviously I will). I feel selfish that I want to meet other girls and find The One that makes me feel amazing.
I'm not sure I really love her that much any more (I don't pine for her when she's not with me, I'd kind of rather spend time on my own), and I certainly don't 'fancy' her any more or yearn for physical/sexual contact. I know it's not 'me' because I still feel that for other girls, so I'm know I'm not romantically dead inside.
We live together though, and she's got nowhere to go (and neither have I) should we split up and need time apart. I don't know how to break up with her, how to go about it without coming across as someone with teenage dreams that there's this 'perfect' girl out there for me (I'm 27 so I feel 'old') and with all of my friends disowning me.
Help?