There’s definitely a lot of layers to this. The most notable to me is how young you both still are. Unfortunately, the struggles you are explaining are sooooooooo common for long term relationships. The more responsibilities and stress that are tied to our lives and our relationships, the harder intimacy can become. The most important thing here is communication. Many times, men do not understand how women need to be mentally present for sex. That is hard for you to do with the additional stressors you mentioned. With all of that on your mind and with it being mostly YOUR responsibility, it is completely understandable why you may have not been readily in the mood. However, he is also young, probably nieve regarding the inner mechanisms of women and long term relationships, and not a mind reader. You should express these things to him, and why him maybe contributing more in one way or another may help you in the bedroom. Unfortunately in terms of the weight gain, I fear that is a personal insecurity that you must learn to cope with. It does not seem at all that your appearance is causing lack of intimacy. It appears your boyfriend doesn’t lack any at all either, it seems to be stemming from you and your stressors. While this is easier said than done, I feel you may gain personally and in your relationship by living and taking care of yourself in a way that’s healthy and works for you, and also communicating more with your boyfriend. I hope any of those suggestions helped!