Is it your heart or your head that's inlove with him? Maybe you should take a step back & re evaluate your feelings. Sometimes, we are so attached to someone that it becomes more of a comfort thing instead of real love. It's almost like fear of change. Nobody likes it, especially if it will bring heartache. I think you are young and your just second guessing what it is you want in life. And that's ok. You have plenty of time ot figure it out. You could realize you really do want to be with him. Good luck.
It's okay to have amivalence about a long-term relationship. I have been there, as have many others. Don't start blaming yourself as having a possible "chemical imbalance". Do you really think it's appropriate to need MEDS in order to be happy with a boyfriend? That is a HUGE red flag. If you have emotional issues separate from the relationship, it would affect other aspects of your life.
It's normal to feel so attached to him and guilty and frightened by the possibility of being without him, but that still doesn't necessarily mean he's ultimately the right one for you. It takes courage to give up a great guy, but don't stay with him just because you're scared and he is a wonderful person. That's the wrong reason to stay with someone. It's not fair to him, and it's not fair to you.
You didn't say if he knows about this. Perhaps you need to start by fully opening the lines of communication. Then from there, you can start to analyze, together, what might be right, and what might be WRONG, with your relationship and being together.
Is it your heart? Or is it an issue with you expressing yourself? (either feeling comfortable or safe) It sounds like you DO care about him, and with no obvious or immediate problems, there's no reason to consider leaving.
Be sure you're not mistaking a lack of emotion with getting used to him (or even boredom). It's very easy to get used to a good partner - they integrate and fit right into your life. Sometimes you don't realize how much you need or love someone until they're suddenly gone. By then it might be too late.
you might love this guy, but maybe inside of you, you might think that he's not the one for you. You gotta really think if you didn't have him in your life has a boyfriend, would you be happy? Would you prefer him being a friend instead? You might be afraid also to lose him all together. But he doesn't have to leave your life. You really need to think about this before you break things off. I've been with my boyfriend for almost 4 years, it happens that I might have temptation because I work with lots of men, but I allways say to my self, that he's the one for me and that we have perfect relationship and why screw this up. I love him to death. I hope things work out for you.