I definitely think you have Dave's motivations down, but I am a little unsure about your voice!

For example, in this thread, I'm not sure why Dave is admitting he was scared. He certainly does open up more to Terezi than other characters in canon, but Dave would never, ever tell anyone he was scared. Getting angry at Terezi for killing him was certainly understandable, but Dave never would have been so blatant with his anger or would ever admit it. In this pesterlog, he is clearly not too happy with her, but he never outright tells her "I am angry and this is why". In fact, he simply becomes extra cagey with her. In this thread, though, he makes his disdain for her pretty clear at the start, rather than just not reply or trying to end the conversation, which would have made the most sense for him.

I'm also not sure why he seems so... Afraid of her in this thread, really.

In general, your Dave seems very upfront. In canon, Dave rarely admits anything without dancing around it for a while, if then.

One thing you have to remember about the Striders is that they are a horribly stereotypically macho family. Bro seems to take this to the extreme, and Dave spends a great deal of his time trying to emulate his brother. This means that emotions are a definite no go for the Striders. This is pretty much epitomized in the way that Dave dealt with Bro's death. It's made pretty clear in canon that while Dave and his brother didn't have the best relationship, they really cared about each other. When Jade asks him if he'd like to talk about it, all he says is:

TG: not much to talk about
TG: this is some pretty serious existence threatening shit going down and some people are going to die i guess
TG: even crazy hard dudes like my bro slash weird covert biological ghost dad

He downplays their relationship a few lines down, too. For the most part, he seems to open up to Rose and Terezi the most, though it's still cagey and veiled in irony and metaphors. This is the pesterlog in which he opens up to Terezi the most, and in which he is the most vulnerable. He still never outright says, "this is how I am feeling and this is why".

Another example is with Davesprite, here. You've got his wordiness down, and Dave certainly does tend to ramble. He just never, ever does it when emotions are even remotely involved. In those situations, he shuts down and his sentences become short and clipped and very, very blunt and to the point. Instead of being wordy about the fact that he'd thought Davesprite was dead, he would have been much more succinct. A simple "thought you'd died" would have been more fitting there, I think.

But at the same time, there are a lot of things you do right: His protectiveness of Jade, his trust in Terezi, his horrible comics and sense of humor, that crippling fear of his own mortality, the way he brushes off criticism and others' opinions, etc. So you should definitely, definitely keep all those wonderful things up! It's really only those two things!