Everyone has different levels of comfort with sharing/knowing/not knowing. Being able to share those preferences with your partners is a good first step.
Maybe a good exercise is for everyone to make a short list of a.) Things I want to know about your OTHER relationship, b.) Things I DON'T want to know about your OTHER relationship, c.) Things I MIND being shared about ME/OUR relationship, d.) Things I DON'T MIND being shared about ME/OUR relationship.
In the MrS/Me/Dude/Lotus relationship there were so many different levels of comfort that it was almost hard to keep track.
Dude = wants/needs to share every detail and know every detail (i.e. everyone hears everything whether they want to or not)
Lotus = ok with sharing every detail, ok with knowing every detail but doesn't NEED to know or share more than the others wants to know - other than safer sex info, level of involvement info and scheduling info (i.e. I am willing to share/hear everything - what do YOU want to share/know?)
Me = I want to know and share safer sex info, level of involvement info (i.e. feelings) and scheduling info. IF you had sex, did you use protection? Are you falling in love in a direction that could change our living situation? How long are you planning on being gone?/When can I expect you back? (For the last set - don't bother asking Dude, what ever he estimates will be approximately 576% removed from reality.) I DON'T want to hear sexual details, I DON'T want my sexual details shared. I DON'T want to hear a minute-by-minute play-back. An outline "We met up at restaurant - food was good, I should take you there. We went back to X place and had a good time, including sex, which was protected by our rules. I made plans to see her again on Friday. No spark yet, but not ruling it out." - PERFECT.
MrS = More difficult for me to analyze, even though I have know him the longest. He will listen to anything I NEED to share ("we had sex" OR "I have feelings"). If he wants to know something, he will ask. If I feel that the other person would be comfortable with me sharing then I will tell him (like about being with Dude or Lotus who have a "share anything" mentality). If I don't know how the other person might feel than I ask "why" he wants to know - what underlying questions about his relationship with me is he trying to figure out.
I very rarely ask MrS about his experiences - the chances of him ever bumping up even close to a boundary without discussing it with me are...NOT. The other weekend we went out with friends and SLeW was sitting between me and him during a scary part of the movie. She clutched at him and buried her face in his shoulder (he is a VERY safe-feeling man). He came home smiling - "She held my hand, it was SOOO nice."
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Once again I find myself composing a blog post instead of a reply...whatever, tonight I will let it stand.