How do I make him feel better?

Ok so my boyfriend and I don’t see eachother that much because of my parents. he gets depressed a lot. he told me that he just misses me and has to deal with the situation. he told me that when he gets in these moods, it doesn’t mean anything and to not worry about it. I feel really bad tho. I mean one day I saw him and he had the biggest bags under his eyes and I could tell he was crying. I keep telling him to be strong and it works sometimes, but like a week later he will get in this depression mode again. I try to be strong for the both of us, because if I were in these depression modes, I don’t think our relationship would be that good. I just want to teach him to be strong , I want to tell him that its ok to think about it , but to dwell on it will only make him feel worse. sometimes he tells me that I have no emotion and that I don’t care as much as he does. but really I ‘m trying to be strong for the both of us.how do I tell him that I care a lot, and how can I teach him to be strong and think positive?? I don’t want him to cry and be depressed all the time I want him to be happy and realize that it will all wrk out and be patient. I don’t want him to be sad :(