Okay here's a concept:
When Ethan said his whole "I'm a single guy with a time-consuming job and a life-limiting condition" thing, what if Rash replied "If being single is your problem then you just need someone to help you with Bodhi and you would take him back? I'll help you." And Ethan agrees and he goes to talk to Pen and Ashley and eventually he gets Bodhi back full time and Rash moves in to help out.
Bodhi starts to call Rash 'dad' too and when he starts school he talks about his two dads and so naturally the teachers just assume that Ethan and Rash are together. Meanwhile, they are actually totally oblivious to this, and totally oblivious to the fact that they basically act like a married couple, even sharing a bed because they both have trouble sleeping (trauma y'know).
But then eventually they are shocked to discover that literally every single person they know thought they were together, and they realise that they'd actually fallen for each other a long time ago, and so they decide to do it for real.