In short, had sex, gf wanted to cum again (masturbating), she did. Decided I would aswell, gf was into it -bending over etc. Just before reaching climax I lean over her so its obvious I'm going to cum on her -though theres about 4 seconds or so where she could object. She doesn't and continues what she's doing as though she's into it, I cum on her ass. 

Shortly after I'm cleaning her up she brings up consent. I feel like what I did was appropriate given the context. She acknowledges she had the opportunity to object but says she felt like she 'had to' let me finish. She acknowledges that what I did wasn't that bad but is still unhappy that I did it. Am I out of order for having done it? I feel like it wasn't unreasonable and that in a relationship consent is more likely to be implied.