It sounds to me like you are under a lot of distress and anxiety lately...Is there anything major going on in your life? Maybe even little things that are building up? Why do you think those "smallest things" are setting you off? Most likely there is something happening beneath the surface that needs to be addressed.
I would suggest therapy and keeping a journal of your thoughts and feelings. Journaling allows you to figure out your anxiety triggers and why you are experiencing all of this depression/fear/anxiety/crying...Counseling can help you work through these issues and cope with them better. I would also suggest writing a letter to your boyfriend explaining as best you can about the situation you are in, especially if you are having difficulty having a discussion with him about it.
When I get like your experiences, it's because of something majorly stressful or anxiety-producing going on in my life at the time. For example, one time I was driving in my car and I heard a song that reminded me of an abusive ex-boyfriend...it set me into an incredibly painful panic. BUT at the time I was stressed out about other things (final exams, graduation) and so this little incident of the song on the radio drove me over the edge...I wasn't properly dealing with my exam and graduation stress and so it was very easy for me to be pushed to my limit...I hope that makes sense
I have a tendency not to deal with my real anxieties and stresses and instead I take them all out on seemingly minor or non-existant "moments."
I hope you feel better today. I know what it feels like and it's the pits