I didn't say it wasn't an in-character thing. In fact, I said...
That first time Peter proposed to MJ, he had not told her he was Spider-Man, and clearly had no intention of telling her he was Spider-Man. And this was *undefined period* after Gwen had died. It was *Undefined period* later that she told him she knew he was Spider-Man, and his first instinct was to try to convince her that she was mistaken. Dude had already proposed to this woman *undefined period* and still didn't think he could trust her with his secret identity.
And then there's Carlie. He cared more about trying to protect his secret identity than about Carlie, which made her so angry that she ended the relationship right then and there.
This is a flaw in Peter's character. And I don't think anyone can argue otherwise. He has trouble opening up. And I don't think it's controversial to say that relationships need people to be able to open up for their partner. And if people can't do that, what kind of relationship is that?
(Edit: There's a reason why you see Peter/Gwen presented much differently in adaptations/AUs/etc.)