Listening is a very big part of it. Since God gave you understanding before, when other people could not, I think I would start by asking Him to help me understand women a little better, and open my eyes to the way that other people see things. I'm not sure how well I will be able to explain what I want to say, since you said you didn't understand when your girlfriend and your mom tried to explain the makeup thing, and they definitely know you better than I do. But I will give it a shot:
Men and women are different, as you know, and generally value different things about themselves, because they have different strengths and different roles. So if you say something that a lady perceives as an attack on something she values, she is going to feel hurt. This (I'm sure you know this part already) is what happened with your girlfriend and the makeup comment. She perceived your statement as an attack on her beauty, saying that her appearance was lacking and needed makeup to improve it until it was acceptable to be seen by your coworkers. What she heard when you made that statement was, "Dear, you're not good enough as you are."
Now, you do not personally need to value your own beauty in order to understand why she was offended. You need to realize that SHE values her beauty and wants to feel like she is acceptable to you, beautiful in your eyes, worthy to be seen by your coworkers as she is. In fact, I would say that most of these "little" hurts that don't make sense to you would make a little more sense if you see the deeper reason behind why they are hurtful.
Imagine an eye and an ear sitting together on a park bench, when a loud siren goes off. The ear is hurt, but the eye is unaffected. Similarly, the ear is unhurt by bright flashing lights, but the eye is affected. Men and women are different, just like the eye and the ear, but by observing and paying attention and listening to one another, they can have a better understanding of why flashing lights hurt the eye and loud noises hurt the ear.
People will sometimes react in a way that you perceive as accusatory, or defensive, or argumentative when they are HURT. Wait, why are they hurt? Those loud noises weren't painful! In fact, you didn't see a thing!