Lots of different things going on here.
First, this does sound a good lesson in understanding your own boundaries and comfort level with things. You can theorize all you want, but you can't be expected to know exactly how comfortable you are with something until you try it.
The next phase sounds almost as difficult - discussing it with your partner. Part of the communication that I expect with my partners is the ability to talk about something that makes one of us uncomfortable without it being a major drama moment. I wasn't there when you brought that up, of course, so can't know how you framed your request, but there should be a mechanism in place to have those chats where nobody feels like the world is going to come to an end.
Respecting each others boundaries is important - being clear in communicating them is just as important. Communication requires not only that someone be told something, but that they truly understand it too. Sometimes that second step is missed and the "Well, I told
you" is thrown out. That also goes to comfort levels too - when someone new comes on the scene, that is the most likely time for envies and jealousies to arise, therefore I feel that it is the most critical time for going slowly and making sure that the person you love can deal with whatever negative feelings they may be having before proceeding.
Sometimes I find it's a good idea, when talking about comfort levels and boundaries, to throw up some hypothetical situations, to "test" where comfort levels and boundaries lie, so that each can know. Surprises are NOT good, both being put in a situation where your lover does something in front of you that makes you feel uncomfortable, but also when you do something that you think is perfectly ok, and you learn later that it made your partner feel horrible. So the more talking and working out that can be done in advance, the better, but allow for the "real world" example to take you by surprise, once in a while.