I've always had secure attachments with my therapists, but I tend to have secure attachments in life in general. It is actually the opposite of dependency. It the ability to have relationship AND be one's self at the same time, to be able to have a healthy reliance on another human being while at the same time feeling secure that you can make it through on your own even when that other person isn't there. Even in real life, the ability for a relationship to end for a variety of reasons is always there; one can fear relationship feeling very insecure because of fear of it ending in any relationship. There are no guarantees.

If a therapist is able to work with a client who is dealing with insecurity about relationships, it seems quite possible they can help a client reach a place where they can live in less fear and find more comfort in personal autonomy over time. But I would suspect it takes time and a therapist very skilled in walking that tightrope between professionalism and personal relationship so that a client understands the real separation between them as two adult human beings. I think the real danger is a sort of enmeshment where the client can't clearly see where the therapist ends and where they begin (and perhaps visa versa in some cases).