<human>: Can you condense the text into three sentences or less?

Me 29F, him 27M. 

We have been together for 5 years and now and have had our shares of ups and downs. However we have been trying hard to make things work again after a recent break up. I love him dearly and he is a wonderful guy, however there is one thing that keeps coming up as a source of tension. This is what I perceive to be his negativity and cynicism.

For example this morning he mentioned that he thought that somebody was stealing the mail because every time he looked at the mail box, the top part was open and yet there was no mail inside. This is a fairly innocent comment, he wasn't angry or upset. However for some reason such comments bother me immensely!! To me this signals a distrust of people in general, which I don't like.

 We have talked about this before and concuded that he would try to be less negative and make negative comments and I would try to be less 'hyper-sensitive' to negativity. He has been trying hard bless him, even starting phrases with the words  ' I am not being negative but...'. However I feel like I have not been able to improve on my end. When I hear anything that sounds negative, cynical or mildly confrontational I just immediately get this distasteful feeling. I feel I am being really unfair to him, but it's like a reflex, and I don't know how to woman up and 'get over it'. Any tips on how to harden up and deal with a negative BF?
<bot>: I am overly sensitive to SO's perceived negativity and cynicism. He is trying hard to be less negative, but I can't seem to become less sensitive.