This game is not a three part very long trilogy taking place over many years (ME) where getting past dealing with a young inexperienced innocent person to the point where a relationship can be one of equals is going to work, theres simply not enough time for that.
So what we have is a group of adults with past lives, loves and traumas and definite ideas of their own. You can agree with them or not, influence them or not, even completely turn their lives upside down - player choice. Not all the companions have previous sexual trauma, Halsin doesn't, Gale doesn't, Wyll doesn't, I don't get the impression that Minthara does and certainly not Lae'zel or Karlach. That they aren't innocent young adults doesn't mean they have sexual hangups. One comes from a completely different culture where family units don't even exist.
This game takes place over a matter of a few weeks and effectively you are in a war zone (not literally but you all know what I mean)for much of it, people in such situations do form strong bonds very very quickly but its not a natural thing to happen.
I wouldn't expect a long term fulfilling relationship with any companion to establish itself over such a short time.
The possibility of one developing afterwards depending on which character you have romanced yes but it won't be fully in place at game end nor should it be, you can love someone without immediately assuming you're going to be together forever and have a cottage with roses round the door, that would be very shallow. What you end with are possibilities....
I think thats why a lot of players feel the abrupt end robbed them a bit.
