A psychological addiction to something is classified as an emotional dependency, and is only considered to exist if, as
jstme said, it begins to interfere with your life or where you're feeling overcome with the desire to try, or have more of, a drug (or whatever you're addicted to). In some cases, that same desire causes people to lie or steal to get it. With any type of addiction - psychological or physical - it is assumed that the user no longer feels they have a choice as to whether they use or not, and no longer do it because they enjoy it but because they've come to depend upon it.
From the sounds of it, you're not psychologically addicted to it because you're not doing it by yourself but because you're with friends and you haven't gone out of your way to do so whilst you're in hospital. Therefore, whilst I can see it's become more of a recurrent thought for you, it's not completely controlling how you think or feel because you're not feeling compelled to partake in it when you're not necessarily able to. You do feel able to live without it and, from the sounds of it, it's more a part of your social life than because you've grown dependent upon it. However, it's likely that you're thinking about it so much because it offers some release from the unhappiness and depression you're feeling - in a similar way to self-injury and such - and so you're more likely to be prone to becoming too dependent. Therefore, with these few warning signs beginning to flag up, I'd suggest that you're a little more careful and make sure that you don't become any more dependent in the future.