I don't have a collar either, but it's so important in every relationship we keep and it works in mysterious ways. I recently ended a vanilla relationship that lasted for three years and could say I trusted him - I trusted that he cared about me, I trusted that he wouldn't cheat on me, I trusted him with most secrets like I would a best friend. But then your question made me realize that, even though I trusted him in these areas, I didn't trust him enough to tell him that I needed the sex to change and that I wanted to explore BDSM (and that I had experimented with it when I was younger). Funny, thinking about it now.

Now, with my current partner, we are working through so many layers of trust its almost unsettling. We've been friends for 10 years (met online when we were young and exploring BDSM). Because we've been friends for so long and have seen each other through various stages of life, I think we trust each other as much as close friends can - which is a great deal! Now that we are shifting to a Dom/sub relationship, it's even more intense because I am learning to trust Him with my body, mind, fantasies and, because that foundation has already been built and feelings are there, my heart. For Him, he is learning to trust His control when we play, as well as my reaction in the sense I won't freak out on Him (since we are both kinda new in r/l). I am sure there are other trust issues for Him, but I don't want to assume...

Considering the importance of our friendship, we both need to trust in each other that we won't do anything to ruin it at the end of the day. I think this is the hardest part - and its probably the reason we never got serious in the past.