This is an obnoxious thing bloggers and people on Facebook do. Not only is it annoying, but it's also grammatically inappropriate. Boyfriend is not a proper noun. Ever. It's just a regular old noun. And, under (almost) no circumstance does it require a demonstrative adjective. Your boyfriend is not the only boyfriend of the world; he is your boyfriend. Just yours*. Congratulations.
He also has a name, so use it. We'll be able to figure out using context clues that Bob, who lives with you and eats the food you make, is your boyfriend. So, don't worry -- everyone will still know that you have one!
Or, if you're too afraid to say his name on the internet, then don't fucking talk about him because chances are none of your readers give a shit anyway. I came to your blog to get a pie recipe not to hear about your relationship.
As you can see, using "The Boyfriend" is one of my pet peeves. Right up there with people you're not related to saying things like, "Mom says hi." No. Your mom says hi. We're not siblings. That would be fucking disgusting considering what we just did.
*Unless of course he's cheating on you, in which case, sucks to be you.