Glad you are sorting things out, Full.
Basically, I do feel that being polyamorous is selfish of me.
Being poly wired is being polywired. A state of being is not a behavior.
I have started feeling guilty and very selfish about being polyamorous.
I am supposed to be inspired by the desire to give love and believe in my heart of hearts that this will be wonderful for everyone involved. When in reality, it was only wonderful for two out of three.
Ah, there's the rub. I think you could mean
"I feel guilty for my selfish behavior in my polyshipping with Matt and Si."
Feeling guilty for HOW you conducted your behavior in polyshipping? Natural to feel under the circumstances. You are coming to terms with it all. It is good you are doing this work and inner reflection.
The "success" of a harmonious polyship hinges on ALL the people's wants, needs, and limits being met to reasonable degree.
You merely being polyamarous and having the capacity to love more than one?
That does not meet all the people's wants, needs, and limits. It is not your capacity but your behavior
that meets / does not meet the needs of others.
If the reality is that it was wonderful for only 2 out of 3? That speaks to the behavior of all the polyship people.
The poly people in your kind of configuration with kids in the mix need to be checking in with each other
all players being up front about their wants, needs, and limits,
all players listening to each others wants, needs, and limits,
all players making the behavior changes required to meet all those things so all can feel good and content in this configuration.
Limits are not just personal limitations within the person -- but nonhuman resources -- time, money, space, etc.
ALL those things must be in place for it to feel wonderful for ALL players. If all those ANDS are not in place? It's just not gonna happen.
It's a hard lesson to learn -- that polymath thing.
All the mini relationships within the larger polyship have to be healthy for the polyship "at large" to fly straight and true.
If not? It flies crooked and could be destined for a crash. So it came to be.
You guys are sorting things out post crash. You will feel a lot of things. Do what it takes to restore order. Learn what you could learn from it. However things turn out for you all polyship wise, I hope each of you (you, Matt, Si) can arrive at a healthy place.
Hang in there.