I love it! I am fully on board with your headcanon that Archer and Trip have a past, and as I babble there, the three of them work best all together. What’s most interesting about these three is how alike they are within their differences, and how that creates a wonderful balance. Honestly, I can see them working, living, and loving together for decades.
After the death of baby Elizabeth, Trip and T’Pol are grieving, of course their relationship is rocky. And of course they would blame it on incompatibility rather than grief. But in a right and proper version of the universe, Archer would notice, understand, and interfere. Archer can be nearly as much of a meddler as Janeway (and Trip), he just hides it better (because Archer cares about appearances way too much). He talks to them separately first. Tells Trip, I’ve known you a long time, seen you with plenty of people, including me. I know you and I know you in love and I wouldn’t have chosen this for you, but here we are. Talk to her. Tell her about the grief, the guilt, the fear, the anger. I know how much you want to shield her from it, but that’s not fair to either of you, and if you don’t say something you will regret it for the rest of your life. Tells T’Pol, no one wants you to be someone you’re not. That’s not what this is. And T’Pol says everyone wants me to be someone I’m not, except maybe you. And Archer gets that look he sometimes gets, like he’s an immortal burdened with knowledge of a future he can’t understand and he’s not allowed to change, but asks her to Just listen, and she agrees. Trip, well, trips, over his words, but once he starts he can’t be stopped (Trip is Actually Terrible at concealing his feelings).
And then, having facilitated their open dialogue, Archer makes to leave but they tell him to stay. And he does, forever.
