How do I stop letting pessimism bring me down?

I’m a positive person and prefer to see the glass half full, my boyfriend is almost completely opposite. For example, my friend gave me a pair of earrings for my birthday, they weren’t really my style but I was so happy that she made the effort to get me something, my boyfriend said “it’s not really anything to be excited about...” or my sister got pregnant, I was so excited for her but her boyfriend is not the most responsible person so my boyfriend said “oh god they’re fu’cked now” and continues to rant about how stupid it is. Today, Ive had a potential employer do reference checks for me and all 3 of my referees called me to say that they have a good feeling about this and thinks I’m going to get the job. The potential employer even said “I’m so happy to have her as part of my team” - I was excited, told my boyfriend and he just told me not to get my hopes up because people can talk sh!t. I feel like whenever I’m excited he just has to poke holes in it... but I know I shouldn’t be letting it affect me. I just don’t know how to change that 🤔