Babel wrote:
It honestly depends on a lot of stuff.
Firstly, mentioning the negative things about yourself can differ greatly, and I honestly don't think all negative things need a reaction? For instance, if I tell my boyfriend I'm not good at vacuum cleaning, then I'm just stating a fact of something he needs to know, because we live together, but I don't need a reassurance or him saying "oh, you can get better at that by doing x and y", because that's not relevant for the negative fact. If I instead talk about how I feel insecure about my arms or something, then I honestly don't want him to compliment them, if he doesn't mean it, because it'll feel disingenuous, and I want him to be honest about what he likes and dislikes about me, because it's easier to ask about opinions on how I dress and look, if he's honest about his feelings usually. I would, however, probably still want a reaction if I talked about my insecurities of my arms with him, but maybe more of a problem-solving reaction ("what don't you like about them?" and "how do we make you more comfortable with your arms?".) than anything. What people find appropriate to react to might, however, differ, and some people might disagree with me about not wanting a reaction on my vacuum cleaning skills, but wanting a genuine reaction for my insecurities about my arms.
With that said, most people are different, and all people have some topics they're not very comfortable or confident talking about. I have a very hard time talking about my own mental health, and whenever I struggle with either thoughts or things in my everyday life, I have a hard time sharing my struggles with my boyfriend before I burn out, which is troublesome. My boyfriend on the other hand talks openly about his mental health struggles, and has no trouble being open about frustrating things or similar. Because we're very different here, we sometimes communicate in a way, the other misunderstands. For instance, when my boyfriend talks about struggling with self-worth, I have a hard time giving him an appropriate reaction, but it's not because I don't care. It's simply because I don't know how, and I'm afraid I'll hurt him by saying something he'll take the wrong way. Instead I sometimes seem indifferent about the negative things he tells me, simply because I struggle to find the right words to convey the answer I want to give him. And while I struggle with this, my boyfriend struggles to deal with me, when I burn out, because I explode in emotions when that happens, and he usually withdraws because his girlfriend before me had to be left alone when she got very emotional, which, to me, seems to be a reinforcement of it being taboo to talk about my mental health, and I take his lack of reaction the wrong way.
So honestly - he might either think it's because it's something he shouldn't comment on, or because he simply don't know how. Whether it's a red flag or not is hard to tell, so the only advice I'll give is this: talk to him about it. If you want him to react to it, or want him to "fulfill a need" you have, you sometimes have to tell the person, because they might not know it's something you need reassurance for.
I've told my boyfriend that I feel it is a rejection of me, when he withdraws, and I interpret it as me doing something wrong. That's not how he intends me to see it, and talking it out makes it easier for me to know he doesn't mean any harm by his reaction, while my boyfriend knows he can react in a different way without me seeing it as a negative reaction. My boyfriend has also told me, that my lack of reaction sometimes makes me feel cold and indifferent, and I've said it's not my intention for it to be that way, but I struggle to find the appropriate reaction, so how would he like me to react when he talks about it? Like, does he want to "problem solve", does he just want reassurance or does he want me to mention the things I enjoy about him? Then I know how I need to try and react, and because he knows I struggle to find the appropriate reaction, he's able to give feedback if I give poorly worded phrases, without having to feel rejected or hurt by a miscommunication, because he's able to say how he interprets it, and I get to try to explain what I mean in a better way.
By communicating about the way we interpret each other and by talking about our needs in specific situations, it makes it easier to give each other room to have our own struggles to work with, while also making it "tolerable" to live with each other, even if we're miscommunicating sometimes.
So again: if you feel like he isn't reacting the way you want him to, maybe talk about how you interpret his reactions, because maybe he isn't doing it on purpose and he might not know you need him to do something else.