I am going to come from this as someone who has experienced anxiety issues and depression issues not regarding poly AND regarding poly situations and managed to work through them.
One of the keys is to NOT fight the feeling. Fighting the feeling only increases it. It's more productive to accept the feeling and then consider what is ACTUALLY causing it (because it's rarely the physical situation we are thinking it is). It sounds like you know what triggered the feeling.
As I also have herpes, I know exactly how emotionally destructive it can be when dealing with a breakout (doesn't matter where-I don't have them on my mouth-but my husband does, we both have the same struggles). It leaves you feeling inadequate and it really reinforces your inability to participate *even if you were invited* in certain activities. It can really take a toll on self esteem for those reasons PLUS there is so much drama about it anyway that just the reminder of having it can set up issues too.
That alone is a perfect explanation for your struggle.
Unfortunately, because the timing happened as it did, your unconscious mind may be associating their time together with emotions that were actually created *first* by the breakout and only exacerbated by them not being "shut out" of activities.
Which then means those feelings all return when they are together without you.
So-what do you do?
First, you let them know THIS-that you've taken time to really assess "WTF is going on with me". And realized that you've inadvertantly created a connection so that when they are together-it triggers the same emotions as a breakout. (the emotions you describe are SO common for people with an active cold sore and well documented so I haven't included links-but you could google it or even ask your Dr.)
that you need some help from them in breaking that connection in your mind and restarting.
This is of benefit to you-but also to them.
Think of some things you can do. For example; when I am struggling with anxiety issues or depression issues and Maca or GG need to be gone for anything (neither is dating someone else currently but Maca has in the past) they will make a point of sending me a text telling me how much they love me AND make a plan for a special thing with me for after. Not necessarily IMMEDIATELY after-it might even be a week later. But-the key is noting the reminder.
"Hey babe! I love you SO MUCH! I am looking forward to our plans to _____ next Friday!"
They might leave me a note in the fridge or on the bed or on my mirror that says something sweet.
Maca will frequently set out a piece of jewelry and ask me to wear it while he's gone.
After the apart time-is reconnect time. A time for lots of cuddling and reassurance.
What I've found is that if I work through this sort of thing, especially AFTER a correlation has been made between some bad experience and some event: I MUHC MORE quickly begin connecting that repetitive event with something happy. This makes the breakdown of the bad correlation more quick as well.
Maybe they could EACH send you a text or leave you a note or something.
Maybe they could each help you make a plan for something special for you to do during their time.
The key is for them to feel like they can be proactive in helping you to build POSITIVE associations to their time alone together and in doing so kill the negative associations.
Instead of them feeling guilty. It's not "I need you to do this SO YOU CAN BE ALONE". That's unhealthy.
It's a matter of them knowing that they are helping you through a mental health "glitch" so that you can be the person they love and enjoy without feeling like they don't care about you.
For you: you have to think of some things that don't stop them from havin their time, but will help you to process that time better. What works for me, might not work for you. But you can figure out what works for you.
For example, if Maca was going out on a date and it was only a few hours of sexy time for him, I might go about making a really yummy, sexy dessert to share with him when he returns (he almost ALWAYS eats something sweet around midnight regardless of when he goes to bed).
I might take a bath, wash my hair, shave, lotion, masturbate, fix the bed, light candles, turn on music etc-so that when he comes home he's got a beautiful smelling room with a sexy wife waiting for him.
If it were GG, I might make a special dinner. I might do the same before bed routine. I might write in our diary a sexy, loving entry.
If you like to read, have one or both of them take you to a bookstore and help you pick out an awesome book to read during "their time" so you have something you enjoy. If you like to crochet or knit-a special project to work on during their time.
Write yourself a letter-telling yourself all the reasons you are loved by each of them and what makes you great as an individual. Write it-during "their time".
Write each of them a letter telling them what you adore about them individually.
Write each of them a sexy story about what you love to do sexually with them or fantasize about or whatever.
Make a gift for each of them or for the both of them-make it during their time together.
(for example: I bought matching towels for Maca and his girlfriend. I went shopping for them while they were out on a date).
"Love As Thou Wilt"