is there anything i can do??

my bf goes away to college, but yesterday he told me that his parents are going to get his dog put to sleep this week because she's really sick & has bad hip problems. I feel soooo bad, mostly because he loves his dog, & also because my bf feels horrible. fortunatly, i've never gone through having to get my pets put to sleep yet, but i know it as to be a horrible feeling. i can only imagine what he's feeling because i love my cats & my dog & i couldn't even think what kind of pain that would make me feel. what should i say to my bf about this?? i don't want to say something wrong that will make him feel worse, but i also don't want to say nothing cause then he might think i don't care. i don't get to see him much, but i will be seeing him this weekend.