I know, I'm the problem, whatever

I can hear how worn down you are by this. "Fine, I'm the problem, I get it" sounds like you've been hearing the same criticism for a while and it's landed as a verdict on who you are, not just a complaint about a moment. That's a tiring place to be. I don't want to pile on, and I also don't want to just tell you it's not your fault. Can I ask what happens for you in the moment she brings up something serious? When you shut down, what's going on inside? Is it more like you go blank, or you feel overwhelmed, or you start thinking "here we go again" and want to get out of the room?

That freeze sounds really uncomfortable, like your brain hits a wall and you're just waiting for it to be over. And it makes sense that you'd want out. I don't think the alternative is sitting there and taking it. There's a lot of space between shutting down and absorbing criticism. You could say something like "This is important and I'm getting flooded. I need ten minutes and then I want to really hear you." That's not blowing her off. It tells her you care and you're still in the room, just not in a way that's working right now. Would that be possible for you, or does even that feel like too much to get out when your brain has gone quiet? I'm also curious what she's usually saying when she's upset that you're not talking. Is it that she wants you to have an opinion, or that she wants to feel like you're actually with her in it?

It sounds like every attempt ends with you feeling like you failed, and that's wearing you down. I'd push back on one thing, though. "It doesn't come out right" isn't the same as "I don't feel anything." When your brain goes quiet, the feeling can be there and still not reach your mouth. That's a different problem from not caring, and it's one that can get better with practice. On the "she'd say I'm finding a way out" part: you may be right that she'd read it that way, and it might help to say that out loud too. Something like "I think you might be right that it could look like I'm dodging, and I'm not trying to. I'm trying to be able to actually hear you." Naming the fear sometimes takes some of its power away. When you say she's better off with someone who feels stuff, are you thinking about whether the relationship can work, or more that you're worn out by feeling like you keep getting it wrong? Either makes sense, and I'd like to understand which it is.

That "already behind before I open my mouth" feeling is a lot. If you're starting every hard conversation at a deficit, it makes sense that the freeze shows up. It can feel like the outcome was decided before you got there. I don't think "I don't know if I'm the guy who can do the thing she wants" is giving up, at least not by itself. It's an honest read of how things feel right now. What matters more is what you do with it. Giving up would look like deciding it's hopeless and stopping the effort. Being unsure whether you can do it, and saying so, is a different place to be. You also said you'd like to make it work. That's worth holding onto, even though you're tired and doubtful. Have you told her any of this, the part about being tired and feeling behind, or has it mostly been running in your head?

That's a useful thing you just noticed. "Whatever, I'm the problem" sounds like giving up, and it closes the door on the conversation. She hears the verdict but not the person behind it, so there's nothing for her to respond to except the bad guy part. On the worry about sounding like you're complaining about her: I'd separate the two things. "You're always bringing up heavy stuff and I'm sick of it" is a complaint about her. "I'm tired, and I feel like I'm already behind before we start, and I don't know how to get out of that" is about you. It's your experience, not a verdict on what she's doing. You can say it without blaming her for it. It might sound something like: "I know I've been saying 'I'm the problem' and that's not fair to either of us. The truth is I get overwhelmed when things get serious, and by the time I try to talk I feel like I've already messed it up. I want to get better at this with you, but I don't know how yet." You don't need to say it perfectly. Even a rough version might land better than the shrug, because it gives her something real to work with. Does that feel like something you could actually say to her, or does the idea of opening that up feel risky?

There's a real pattern in what you're describing: you try to say something true, she takes the part that confirms the story, and you end up back at "I'm the problem." That's exhausting, and it makes sense that opening up feels like handing her ammunition. About sounding like you're reading off a card: you don't need the exact words. The script was just a starting point. What usually sounds scripted is when the words are polished and the feeling is missing. If you say it in your own rough way, even with awkward pauses, it'll probably come across as more honest than anything I could write for you. You also don't have to do this in the middle of a fight. Picking a calmer moment, when neither of you is already braced, might make it easier to say and easier for her to hear. You could even just say, "Can I tell you something I've been struggling to say?" and see how she responds. If she does take it and run with "so you admit you're the problem," what would you want to say back to her in that moment?

That's fair, and I hear the sting in it. It's easy for me to hand you lines when I'm not the one sitting across from her, and I don't want to act like I know exactly how that moment will feel. I also notice you've come back to "whatever, I'm the problem" a few times now, and each time it seems to be the thing you reach for when a conversation gets too hard. It's kind of a way of ending it before anyone can get hurt, including you. I don't think that makes you a bad partner. It sounds like a pretty old move that's been protecting you, even though it's costing you a lot. So maybe the goal isn't finding the perfect thing to say to her. It might be just noticing, in the moment, when you're about to reach for that line, and being able to say "I'm not okay right now" instead. That's a smaller step, and you can practice it on your own before you try it with her. Does that feel more doable, or does it still feel like it would get twisted into something else?

You keep landing on the same spot: you try, it doesn't land, and you're back to "whatever." That's a discouraging loop, and I don't think you need to solve it tonight. I'd gently point out that "whatever" is what your mouth does when you're flooded, and that's exactly why practicing on your own makes sense. You don't have to get the words right in the moment. You just have to notice the moment a bit earlier, maybe when you feel the quiet start, and that noticing alone is a real step, even if it doesn't come out perfectly. I'm also hearing that you're tired, and that you don't entirely know whether you're the person who can do what she needs. That's a lot to carry, and it's okay to not have answers yet. If it would help, we could think through what you'd want her to understand about you, separate from what you think you owe her. Or we could just stay with how heavy this has felt. Which would be more useful right now?