We see the idea of "once an addict/alcoholic, always an addict/alcoholic' on here quite often, and indeed it's pretty much become an accepted mantra in our culture, due to the work of the AA.
And don't get me wrong - AA clearly help many, many people in their recovery, so clearly that way of thinking helps many.
But it's no longer the only model of recovery out there, and it's not a view all of us subscribe to. Indeed many of us find it quite limited, damaging.
I got used to have some issues around alcohol abuse, and got sober using the SMART model of recovery, which does promote lifelong sobriety, but does not encourage me to thinking of myself as a lifelong alcoholic.
Some of you might be interested in exploring their ideas.
Anyway, OP it's entirely your choice. I wouldn't be put off by someone who had used heroin years ago, provided he was in recovery now and seemed responsible and realistic when he spoke about it.
But we all look for different things in a partner. You are allowed to call time on the relationship at any point, for any reason. Others may not do the same, but really it only matters what you think about this....