It may well be that you contacted her more than she wanted, and only you know the content and tone of the content - it's entirely possible she felt harassed if you repeatedly contacted her, but she's fostered that by not replying. I can understand your anxiety increasing without acknowledgement or response from her. I see it like a kid with mum who hasn't responded, they often then start with "mum, mum, mum, Mum, MUM!!!". Yes mum feels harassed but if had answered the first time... And for clarity I'm using this as an example, not saying your in the midst of maternal transference.

It's ok for her to want to set boundaries about contact out of session, I know you know this, but the way she's done that isn't ok because she's played on all your fears. In the above example, if mum started withdrawing from the child as a punishment we'd call that abusive behaviour. She should, as other posters have said, give you space to explore what need you're trying to have met with contact and agree to keep talking about it, and to talk through what her tighter boundaries mean for you (eg her pulling away).

In answer to how you detach? Ideally she offers you enough consistent care and nurture (in session) to allow you to trust that others will do the same and, naturally, your attachment to her lessens. Or you make the decision to keep yourself safe and find someone with better boundaries who can give you the care you need. In other words, in exactly the same way we detach in real life.

I'm sorry you're hurting, this stopped being about your behaviour with in between contact a long time ago and is about her not knowing how to work with you properly.