Many people seem to find Heroin extremely addictive, but for me, I can control my use for many years now, quitting now and then and not having it too hard with the WD and once I'm clean for a while enjoy it once again much more again!
But anyway, yes, addiction is a huge possibility.
The puking and sickness is normal, most people experience this when they first use Heroin - if you would use it 3 to 5 days in a row you would not have that sickness anymore; only then the great effects of the drug surface, if you still get sick from your Dope, you won't be able to get euphoric from it...
If I'm not mistaken, it has to do with the defense mechanisme of your body, which eventually creates a shortness of oxygen in the blood and that's what makes you puke in the end - indeed because the drug, even in small amounts, is too much for the body to handle as for the body it is seen as a major toxic that needs to be broken down... So that's why it won't give you any euphoria as long as the body is not used to the Heroin.
The only way to get rid off this discomfort is, like I said, to use it 3 to 5 days every day until you don't get sick anymore.
But just quitting now you're ahead of the game seems a better idea. I'm just saying, what I pointed out is the only way to get rid of the sickness, not by using once a week, and the only way of being able to get euphoric, by letting the body accumulate to the drug...