In the initial stages of the relationship, I also thought that there was no one I could connect to emotionally or sexually as well as the addict.
Addicts love-bomb you in the initial stages of the relationship -- this can last anywhere from 2 weeks to 2 years. It's easy to get stuck in toxic relationships if you're lonely to begin with -- people need people. But after about a decade, you'll find yourself one day living with a man who is actually a total stranger, because you were not looking at the whole man, just a part of him that he wanted to be or wanted you to think he could be. You also wanted it too. The reason you wanted to desperately for him to be anyone... is because your cup is empty and always has been empty.
You'll find yourself, as I had found myself, living with a stranger who you only have sex with because you think you have to, who doesn't fulfill you emotionally at all. Then you realize that you were filling your cup with air -- at least, that is what I realized.
Addiction is progressive. Not every lonely person is a codependent. But being in a relationship with addiction is going to make you into one -- you'll get sick.
Maybe try to re-wire your brain: every time you think about him, do something else, like take a jog, play an instrument... anything to distract you that is also going to be good for you.
Do re-read the Robin Norwood book if you can.