I have a very simple thought abut Theo/Brett + Liam, whether as a threesome or just one of them with Liam:
Theo - He and Liam would have a lot to work on, no doubt, and it wouldn’t be easy. But they’re both stubborn and love each other, so they’ get there come hell or high water. They have their emotional crises (particularly Theo) and they fight, but that’s how they work. They’ll settle after awhile. KEY: Their fights and crises revolve around them taking care of each other, even if that means fighting. The focus is healing.
Brett - I think it would be harder for Liam to adjust with Brett, and - honestly hopefully - for Brett to adjust too. (Boy should need some personal growth tbh). I’d expect just as many emotional crises and fights, though more verbal than physical ones. KEY: Trouble with Brett would mean Liam withdrawing and putting up walls.
Liam and Theo were practically inseparable - whether they liked it or not - during the ghost riders and again - much more happily - during the anukite. Theo did a sh*t ton of damage, but Liam was there.
- He saw a snapshot of the decade of torture and conditioning Theo went through when the Doctors took him and Hayden.
- He brought him back from Hell (and deals with Theo’s night terrors)
- Wether he knows what was in Theo’s hell or not, he witnessed first hand the effects it had/has.
- He and Theo were joined at the hip during the ghost riders, so he saw first hand Theo’s very quiet crisis of realizing he actually cares about someone else and wanting to keep them safe.
- They were together again during the anukite and Monroe mess. Theo kept him safe, grounded him, and kept others safe from him.
Liam witnessed and experienced first hand Theo changing and trying to be a better person. By the time they would have gotten together (late show/post-show) he would have been there for everything post-hell and post-doctors. There was a long process of Liam learning to trust Theo and Theo learning how to care.
This isn’t how it went down with Brett.
- Brett was the ringleader in actively kidnapping and abusing a freshman - a 14/15 year-old.
- The trauma he caused affects Liam similarly to the berserkers and it’s obvious from the zoo episode that Liam hasn’t worked through it.
- This abuse may be what triggered the massive flare of his IED that led to him destroying a car and being expelled.
- From the very first we see that Brett really has not changed since Liam switched schools and continues to taunt and try to hurt him.
- Brett does stop this behavior, but Liam wasn’t there.
Liam was not there to witness Brett change, however much or little that he did change. He never knows why Brett abuses him, he does not see Brett become a better person. While it seems that Liam does care about Brett during the Monroe storyline and is deeply wounded by his and Lori’s deaths (ret-con that in the case of a post-show relationship), Brett does not earn this in any way/does very little to earn this.
Liam witnessed Theo change and actively helped him learn how to care for someone.
Liam did NOT witness this with Brett.
So I think a relationship including Brett would lead to Brett accidentally triggering Liam’s trauma from the abuse he caused, several times. Maybe this would cause a lot of fights, but personally, I think Liam would shut himself off from Brett whenever it happened. He doesn’t want to hurt Brett, but dear f*cking g-d we saw what happened to Liam at the zoo. If it’s threesome, he would probably rely heavily on Theo for comfort instead of letting Brett try to help him.