If it is really what you described, I think this phenomenon is not only caused by you, but also by your girlfriend. No matter how thin an adult boy is, he weighs at least 90 kilograms, so it is easy for you to be picked up by your girlfriend with one hand. You and your brother, two adult men, can be easily picked up by your girlfriend's two hands, which shows that your girlfriend is really powerful. Very powerful, and your girlfriend should also be a very powerful person. After all, with such great strength, even if you don't know taekwondo or boxing, you can beat the people who come to trouble badly. After all, the strength is there, not just talking. As for you, I think you can go to the gym and do more exercise in moderation. Instead of letting you exercise a lot in one breath, it is better to exercise as much as possible while ensuring your life and health. You shouldn't care too much about the fact that your girlfriend is better than you, which is not good for your health. You just need to remember that your girlfriend likes you and won't dislike you because you are weak. This is the trust that couples should have, so that your's feelings can last for a long time. Finally, what you said is too thin. Some people can't get fat no matter how they eat. Those are people who lose weight easily. Some people don't eat well and are too picky about food. They only eat what they like and don't eat those that are really nutritious. Although such people are not easy to lose weight, they are still thin. I don't know what kind of person you are, but I think if you are the second kind of person, you should eat well and mix meat and vegetables. Drink more milk and supplement some vitamins your body needs, so that you can become a person who is not very thin, not to say that you are not thin, but if you are too thin to have strength, then you are not worth it. Since you want to have strength, you should take good care of your body and make yourself a healthy person.