Hiya. I'm new here. I've joined because my gf is addicted. I believe the standard behaviour is to just chip in, so for what it's worth:
Many men I know are led by their instincts. If we like someone we want to touch them. That doesn't mean we should, even in a long term relationship, I'm just saying that most of us WANT to, most of the time, especially if we have real feelings for our partners.
I personally like to touch my girlfriend often, though it's never seemed inappropriate. It's important for us men to let our GFs know that we fancy them, and a gentle touch, squeeze of the hand, kiss on the cheek is enough to reinforce that sentiment. To quote Monty Python 'You don't have to leap straight for the clitoris like a bull at a gate' though that is many men's basest impulse, and I think a gentle shoulder rub, or a waist-circling cuddle from behind can be universally appropriate (as long as you're not in trouble with her) and will also give the opportunity to find out how she's feeling at that particular moment.
If she were ill, for instance, I wouldn't, for the simple reason that if I were ill, I wouldn't be up for it either. Sex, and all the preamble that leads to it, is something you both have to want, and while I want to do it pretty much all the time (she's just delightful), I always try and be sensitive to what she wants. Ultimately I don't want anything that isn't offered freely and with enthusiasm (though it doesn't stop me broaching the subject verbally as often as I think i can get away with it - she's become a dab hand at gently swatting me down without me feeling rejected, hurt or neglected)
What this comes down to, if you ask me, is sensitivity. If you care about your partner, you'll be sensitive to her needs and feelings, you'll pay attention, and in doing so you'll get to a point where you just know whether or not the time is right. You definitely won't sulk about not getting sex, and you won't play a manipulation game to get your own way even if your partner is poorly.
That's just bad form I reckon.