My Bf hasn't been able to climax with me at all since we been dating 5 months.

My bf 19 and I have been dating for 5 months and we have sex now every day to ever the day but during all that time being today he hasn't been able to cum with me he says he has to finish alone by himself to cum. I talked to him about this and i am thinking on leaving this relationship because it is messing with my head. I mean am i no good? am i ugly and gross him out he has told me that this hasn't happened to him before until we started dating. His reason is its all him not me should i just leave him? the sex thing has started to mess with our relationship don't get me wrong though he fucks me real good to seeing stars but it all stops when it looks like he just changes and wants to stop right then and will go shower n jerk it idk i need help