In Dragon Age specifically? Most Andrastians are straight/sexuality never talked about, and if you're a Templar (in any sense of the word, i.e. Seeker), you are definitely straight. Cullen, Cassandra, Alistair, Evangeline. All straight (Evie could be bi, but I doubt that will ever happen). Templars are never LGBT, and Andrastians only rarely (when sexuality is brought up of course).
Warriors, also, tend to be straight. This will change with Iron Bull, but I'm already afraid of his "promiscuity". Segue!
LGBT characters are rarely the type to "settle down", and the possibility of talking about one day starting a family never seems to come up with LGBT characters.
And I seriously hoping that this whole "Dorian can be, like, totally your gay best friend thing" be proven false. Flamboyance =/= LGBT (though modern media in all it's forms often support the idea). Also, while I'm on the topic, this whole "GBFF" thing bugs me, do people segregate their other friends like that? Do people introduce their friends like "this is my black best friend, Darren?", no, that would be racist... (EDIT: Sorry for raging).
In general media? Gay characters should not be attracted to every single specimen of the same sex. It doesn't always work like that. If we ever see some non-LI gay NPCs, I hope that they don't follow this trope.
Also, not only are male "bi" LIs mostly going for women, but a lot of them only go for males because they begin to look beyond sex. Anders talks about what is inside matters, not the outside, Kaidan is looking to search for something deeper with someone he already cares about, etc. While those are nice from time to time, it'd be great if we have a dude tell us dude PCs that we are HOT. In caps. Guys like to feel sexy too. There's a trope somewhere in there, I don't know how to quantify it. Maybe that those LIs are not really bisexual but heterosexual and biromantic. Also, these, in DA, are the human bisexual options. Male elves call male PCs hot, Male humans don't...
The Serendipity thing (i.e. drag queens/kings = transgenders when they don't. Also any form of crossdressing (whether for performance or not) being a joke all the time.)
Also, male LIs tend to be more "unconventionally attractive" while female LIs tend not to be (only "pretty" elves and humans).
Dwarves =/= Love Interests (three games we have had a dwarven companion, including Awakening, and while Varric and Oghren are sexual beings, they aren't sexual for a PC. Sigrun was also another possible LI ignored, not even a flirt from a PC to be found).
Sorry if I ranted a bit.