As an addict, I will give my side of it with dating people who are "straight."
It almost always happens because they see some kind of tragic, flawed beauty in me, and think somehow they can "save me."
(I'm a guy, have two degrees including a masters, and would probably be somewhere if I didn't love dope so much. As my bicycle dealer said when I graduated from college "You probably would have made Dean's List if you weren't so fucked up." "Uh, I did make Dean's List." "Well shit, I hate to think what you would've done if you weren't so fucked up." And I mean dope as in opiates, as well as lots of other substances)
As far as my relationships, there is either something about me that seems to be attractive to rich hipster chicks who moved to the city to slum it, or really legitimately attractive older women who see that "tragic beauty" in me and feel like they can save me or some shit like that.
The worst of this was dating a 38 year old woman (who actually went on to work for the FBI - yikes) who would just totally enable me, give me money for drugs and alcohol, give me a place to stay when my power was cut off from non-payment, look the other way when I was in her medicine cabinet rummaging around, yet would always take me back. This was a fucked up situation because i was only 22 and pursuing my Masters degree, and she thought it was more important that I just "make it through" than me getting straight, etc... So in some respects it would have been better if I would have just dated another addict.
In the end, I probably taught her a good lesson about not saving people as I'm sure she feels like she got burned bad by me, but at the same time, I feel badly about totally taking someone for everything they would give me and then some.
I don't really think addicts should date anyone, and I haven't necessarily got it under control or anything, but at least I go into relationships with total full disclosure now so they aren't entertaining any notions of me being a good person.