For me, "attachment issues" just means that when I was an infant. my mother was very ill, both physically and mentally, and just couldn't tend to me in a consistent way. The people who study such things believe that an infant who lacks consistent and loving care will have hurdles to overcome in relationships later in life. And from there the theories go in all sorts of ways. And the treatments are many as well. Can you ask your t about how they intend to treat it? There as some (as noted above) that thing that attachment to a t is the best way to heal. There are others that offer week-long intensives with family members. There are treatments such as EMDR, Brain Spotting, SE that do not promote attachment to the t. And there is psychoanalysis that is intensive as well. And there are group therapies, DBT for one, that also help some people.

For me, understanding why I have attachment issues has not been very helpful. And the kind of therapy where one is encouraged to attach to the t has not been super helpful either.

I hope your t is able to suggest a plan of treatment that makes sense to you.