Dealing with my boyfriends depression

Whenever i have conversations with my boyfriend about our relationship he takes it as an attack instead of a conversation. Because of his depression he thinks he's a shitty boyfriend and as soon as I bring any small thing up he immediately gets super sad. I pretty much have to retract and say things like "it's okay it's fine it's not a big deal" "I'm already over it" "I'm sorry I over reacted" and stuff like that to make him calm down.

He's an amazing boyfriend but I find it hard to work on our relationship when he does this.

Having to comfort him when I was initially the emotional one is hard to do over and over again. I pretty much have to bottle my emotions up to make sure I don't set him off.

Does anyone have any advice on how to approach him without him thinking it's an attack??