Having sex isn't the be all and end all of relationships. Sometimes it doesn't work out despite there being a deep love for one another. It might change, it might not, but if you're invested in a future sex scene for literally anyone know that you're likely to be disappointed as it's not the intent for the game to cater to explicit sex. It's just there as I need it because... sex is a thing people do.
Tyson in particular is... a special case but I hold all the cards as to why. Remember, he has kept saying that he's not gay, so figuring himself out is absolutely a keystone of his route. They may not get to sex if they end up together because there's just so much other stuff to sort through first given their history.
There are no other potential sexual candidates on the table outside the main cast. This means that Benson and Oswin are out, plus any other characters that may show up after route selection.