I feel for you, but I agree with RP that just because you were first doesn't oblige your wife to give you preference.
There's a very famous saying: "All's fair in love and war." This really means that everything is so bloody UNFAIR that it makes absolutely no sense to talk about fairness.
Unfortunately, you have (I think) 2 - maybe 3 - disadvantages in this set-up:
a) I guess that the other relationship is newer for your wife than the one with you? (Or living with her is newer?) This would mean that there's a degree of new relationship energy (NRE) working in the other woman's favour. [There is a SHITLOAD of comment/advice/experience on the subject to be read on this board, if you want to use the word search facility.]
b) Trying to put myself in your wife's emotional shoes, I can imagine that (especially at the beginning of a relationship - or the beginning of being allowed to openly live together) I would rather go to bed with somebody with whom I'd spent the evening already (with romance building up over that time) than trod off to an empty (maybe cold at this time of year?) bed all alone to wait for somebody who's going to stumble in later (maybe after I've fallen asleep?)
c) Here I'm guessing even more. What are the practical dynamics of the child-bedding arrangements? This is a 5-month-old baby. Does the baby sleep with Trina? In a room nearer to the gf's than to yours? Trina might be doing any of the following:
i) prefers to sleep as far from the baby as possible. Not so far that she won't hear the crying whenever the child awakes.
ii) prefers to sleep as close to the child as possible, possibly in the same room.
iii) prefers to sleep in the same bed as the child.
In the case of iii), there are further variations:
1) The gf loves the baby, too, and is happy to share the bed.
2) You are tired after your evening shift, maybe want to make love before sleeping, but are less patient with interruptions from the child. (Does Trina breastfeed during the night?)
3) Your sleeping patterns affect the baby.
You write that Trina has said that sometimes she prefers to be with one of you, sometimes with the other. Maybe you should be patient. Maybe your time will come...
I hope it all works out for all of you (especially the baby).
If I can't dance, I want no part in your Revolution.
- Emma Goldman Anarchist and Polyamorous par excellenceThe person who says something is impossible should not interrupt the person who is doing it.
- old Chinese proverbAnd the day came when the risk to remain tight in a bud was more painful than the risk it took to blossom.
~ Anais NinI'd rather have a broken heart / Than have a heart of stone.