From your point of view, a guy masturbating at home when you're right there is a giant dick-slap-in-the-face. Only you wish it was his dick.
It's not, though. It's just the flaccid backhand of life.
For you, this might feel like a rejection, like you're not pretty or arousing enough to merit the amount of effort it would take to have sex. It might feel like you're being ignored or passed-over. Why would a guy settle for something much less exciting and lubricated when he has the whole package right there?
It's easy to take that personally and assume your boyfriend doesn't want to fuck you.
And … he doesn't. If he wanted to fuck you, 9/10 doctors say he would.
Sometimes, guys crave sensations that you're not physically capable of giving them. On certain moonlit nights, they just want to beat the shit out of their dicks with their gnarled, scaly hands. They already have a premeditated masturbatory pressure and speed they know and love, and it's easier to self-gratify with that than to train you to do it for them.
Plus, even if you were willing to mutilate his dick with the fervor he wants, many girls and guys wiill still suck at giving handjobs. It's just not the same when someone else does it. The other person comes at it from the wrong angle, the stroke's all wrong and the grip is nothing like his college buddy's five-fingered magic grip. I wrote a whole article about this. Check it out.
It's like … you know when you get horny in your clit? And you know exactly how to alleviate that because you have years of masturbatory experience? Your knowing, precise movements make the cut, but your boyfriend's fumbling hand dance probably doesn't. Or when all you need in the world is your vibrator? Your boyfriend's dick doesn't vibrate, and therefore you don't seek him out when you're looking for that specific feeling.
It's exactly the same for him; your limp-wristed, half-assed attempt at a hand job is nothing compared to what he can do for himself. So, it's just him following his desire for a particular sensation you're incapable of giving him. Fine.
Other times, guys just don't want to bother you. Maybe you're asleep or cooking dinner or shaving your secret mustache or recovering from a butt-hole wax.
If men were any fun, they'd just hook up with you in the midst of your weekly conversation with the debt collector or whatever other activity you're doing that isn't sex, but they're not. Although most girls actually want to be bothered with sex because it makes them feel desired, most guys avoid doing that because it seems pushy and invasive. Most guys want girls to want it, visibly. Otherwise, they feel like predators. They don't want to be creepy. And that's nice, isn't it? Real cute.
A third reason why dudes make this idiot mistake is that they're horny for something else that isn't you. Maybe their hot friend is making them privately horny and they don't want to let that energy out on you. Maybe you're a 105-pound brunette but they're into the mood to see an obese MILF get gang-banged by tall men wearing glittery capes. What are they gonna do, ask if you want to watch that porn with them? Even if you do, they're worried you'll think they're weird for being so turned on by it. And they're frequently so disgusted by their own fucked up fantasies and desires that they don't want to burden you with them. They'd rather just cum in a tissue and go back to what they were doing without confronting the potential shame.
A lot of girls want to get woken up with a dick pointed at their eye. They wanted to penetrated while making mac and cheese and to be eaten out while they're Skyping with their boss. It makes them feel irresistible, and that builds their confidence. But that's asking a lot of dudes, who sometimes just need to to cum without worrying about how it is for the other person.
Now, for dudes who have gotten this far in this rant: first of all, welcome. I just want you to know that jacking off when your girl's home makes her feel pretty, pretty shitty. To avoid this situation, make sure you know how far you can take it when it comes to acting out your arousal. You may find out that she's DTF in a lot more situations than you previously thought. If she says "I want you to wake me up fucking me," then do it, god damn it. She's telling you very clearly what she wants. If she never mentions it, don't do it until you know if she's okay with it or not. However, through talking to her, you might also find out there are very specific situations where she does not want to have sex, like after she eats Indian food, and then you know it's cool to slap your cock around by yourself.
For girls: This is one of those situations where can take it kind of personally, but not to the point where it starts to eat away at you and make you feel horrible about yourself. After all, chances are it has nothing to do with you. But do take it personally enough that it makes you realize you need to communicate with him about what you both want. You might have to make it clear to him that you're down to fuck more than he thinks you are, and you'd rather take care of him yourself than make him cum into the empty white expanse of the house toilet.
At the same time, realize that guys have their own, very unique and specific sexual needs that you can't fuck with no matter how hot you are or how much of a vacuum your pussy purports to be.