So I've really set my eyes on Brynjolf of Riften...

But I can't start any romance with him? All he wants is to give me quests...

Am I stalking him in vain?

There is a list of those you can marry somewhere on here near the first few pages. If his name isn't on the list then you are.

He is not in the list D:, so you are stalking him in vain D:

Since you stalked him in vain I'll let you marry me. Inbox me if you accept.

I think there's a mod that lets you add unique NPC's as followers and spouses (if you're on a PC). I'm trying it on Brynjolf when my PC is repaired, I've waited ages to marry him to my main character.

Edit: http://skyrim.nexusmods.com/downloads/file.php?id=4690 It should work when you complete the TG questline.

All you wanted to know about http://www.uesp.net/wiki/Skyrim:Marriage but were afraid to ask.

Also, I'm not sure you really want Brynjolf. At some point in the future, you'll come home from a day of bandit slaying and before you can say hello, he'll say, "Sorry lass, but I'm too busy to talk right now."

Better to find somebody of industry.

On my latest char, I'm thinking of marrying http://www.uesp.net/wiki/File:SR-npc-Bothela.jpgin Markarth. The benefits are numerous!
1. She has a thriving business in a swank shop;
2. She has comfy rooms in the back of the shop;
3. The location is convenient to the forge, unlike Vlindrel Hall.;
4. She has a personaility (or is it poisonality?);
5. She knows how to mix up a very useful elixir;
6. And there's always Muiri...