noodlebee, I managed to get myself into a similar situation a few years ago and while I don't regret the final decision I came to - as it resulted in the greatest relationship I've ever experienced and it's still going strong - there are plenty of things I'd have done differently.
All in all, you've got to make the decision that you believe to be most to your advantage but I can't stress enough that someone will probably be hurt by the decision you come to. Be gentle with their hearts and sever the ties completely with the one that wasn't chosen.
And while I certainly may have missed it in your posts, I don't remember reading anywhere that you and your boyfriend tried to work out these issues and keep things interesting. You say that you don't have much beyond cars and gossip to discuss with your boyfriend but have you two honestly tried to make things better?
How sure are you that rather than another lover, a bit of change may be in order? If you two have tried to no avail and your issues are beyond repair then you I think you should end things with your boyfriend either way.
And how sure are you that this roommate of yours is who he presents himself to be? Have you known him long enough to really trust him?
...
Good luck.
