From my own experience: If I don't like the metamour I can't handle their relationship with Breathes. If I like them then things are MUCH better. I can handle them cuddling, hugging, kissing, etc.
Breathes and Possibility, my primary and secondary respectively, seem to handle this very well. Last night we were at Possibility's place. There were four of us in the basement. I was holding Possibility's hand while my other arm was around Breathes. We don't get a lot of chances to do group things together (some of it by my choice, some due to circumstances) so when I'm up to it I take the opportunity and run with it!
Breathes and I have talked about it and as long as he knows I love him he's good with the way things are going.
It's best to work through your issues one at a time. Simple things like letting them give each other a hello/good-bye hug can help immensely! It lets them know you really are trying to overcome these things and it gives you an opportunity to work through it a little bit at a time without overwhelming yourself with emotions.
Search for boundaries, rules and any other word you can come up with. There's lot of advice on here for situations such as yours.
There are as many ways to do polyamory as there are people practicing it!