<human>: Can you give me the gist of the text in a nutshell?

I'm a 19f and my bf is a 20m and I'm writing this from his throwaway. This is the first real relationship for both of us. We have been dating for 3 weeks and, as the title suggests, i've been having doubting feelings like: 'are we gonna last', 'this in turn is making me think that because I have these thoughts maybe I don't like him as much as I should even though I think he's amazing', as well as 'should i work on myself a little bit more for even having these thoughts'. 

My bf thinks I'm being crazy and that these feelings will go away as time moves on but I'm extremely doubtful. Even before we started dating there was this hesitating feeling about the relationship but I am known to avoid romantic feelings so I ignored this initial thought and went on with the relationship anyway. I am so confused and stressed out about this and its putting extra strain on our relationship. I feel like we should end things now before we both get more attached to each other and it ends up being harder in the long run. 

Although I have these thoughts, when I brought this subject up to my bf and we started talking about it I became really distraught and was crying like he was the one breaking up with me....Idk what to do and just want to stop stressing about this. My bf is a great bf and treats me the way I want to be treated, but i just can't help feeling like something is not right. What should i do?
<bot>: Been dating for 3 weeks. First relationship for both of us.  Can't shake doubts about how long this relationship is gonna last despite boyfriend not doing anything wrong. What do I do?