First off, who would name their cat Taco? Now that's out of the way...
I don't think your doomed I think your confused. Don't listen to the people that have such shallow unfulfilled lives that that have to come here and spout off at the head. Listen to your heart.
To be clear, please try and separate the difference between your heart and your pants first. Just because this old flame came back into your life that is no reason to flush away what appears to be an otherwise solid relationship.
What would happen? You would be helplessly and totally into the "friend" for awhile ya, but then it's going to hit you like a ton of bricks "Hey, I could have done something about this years ago but I chose not to" So when the newness dies down and you have had your fun, your right back at freaking square 1 again.
Joint vehicle, Joint house... whoah, you obviously "thought" you were going the distance with this man. Look at everything carefully before you make a decision based upon attraction? Is it the whole package? Can you fix what is broken with your bf? Have you had a "date night" in awhile?
It's normal for you to have a feeling or two for your old crush, nothing wrong with that, that's why they are crushes.. Know it for what it is and avoid a potentially life changing experience.
Good Luck, you sound like your stressing!.