It sounds like you each have your own individual beliefs and perceptions about how relationships and displays of affection "should be" and they are not exactly matching up.
Sometimes people who are very comfortable with outward displays of affection just do not get that other people find that "too much" or feel like they are intruding if they are near someone who is being demonstrative. She might even lean toward having exhibitionist tendencies. Just tell her you are not a voyeur, and that you look away because you feel you want to give them privacy. I think it is perfectly fine that it makes you uncomfortable to see them being physically intimate, but she should know that it is out of respect for their privacy and the fact that voyeurism is not your thing, and isn't based in jealousy or possessiveness.
It also sounds like you are the type of person who likes your relationships managed separately and somewhat compartmentalized, while she likes having a lot of togetherness and would probably really dig being part of a big poly commune. To me, for her to say, "these are not two relationships" doesn't make any sense at all. Sure, you and he are friends, but she is in two relationships -- and you are only romantically dating her, not him, so why does she think it's all one big relationship? There are actually more than that: You and her; him and her, you and him (as friends); and all three of you together. That is FOUR relationships and each dynamic needs to be nurtured independently!
Why is she forcing you to change your comfort zone when she is unwilling to to make changes to her own comfort zone? She is being selfish and demanding. For her to call you a wet blanket is very inconsiderate of your feelings.
If I were you, I would show her this thread and ask her to add her perspective on it so you both can get more responses that help both sides of the issue.
Last edited by nycindie; 04-10-2013 at 03:25 PM.