Wandering, I think there are two ways of looking at the outside contact issue and both are related to what happens within the sessions and where you are in the process. If you feel "held" by the therapy framework, if you have a trust that sustains you between sessions, then the work done during sessions is often enough to contain the attachment: it doesn't grow exponentially outside of session times in ways that disrupt your life.

But if you don't feel that security, that sense of being held within your therapy, then feelings of need may intensify between sessions, and without the opportunity for contact, may become a frustration (or with lots of contact lead to heightened dependency).

My personal view is that a client isn't yet "ready" for attachment when this is the case, and that more foundational work needs to happen within sessions before intensifying the work. Too soon attachment for whatever reason can easily provoke deep dependency needs. With the right therapist, it can be handled, but it's challenging work. A really well-trained T paces the attachment and slows down the work as a safer alternative, unless they practice in an intensive attachment modality--but that doesn't seem to be the way your T practices, given his no contact policy.

Only you and your T together can determine if you and your therapy are ready to sustain an increase in attachment. It sounds like your T understands attachment; so it may just be about timing for you. I do think it is best when a client can be very reflective and open about the feelings they're having in order to use them as a guide to the pacing. Attachment work isn't like jumping off a cliff--it can be monitored and adjustments to the pacing made in order to stay within a manageable range of feelings. It just requires you to be willing to be open with your feelings and not be misled by what you think you "should" feel.