If your lovemaking has gotten to the point that she can knit a complicated sweater (while you're hard at it) without her dropping a stitch, the problem may not be her attitude toward sex, but your method.
Yes, by now she's gotten accustomed to your size. But that shouldn't affect her reaction to your lovemaking.
What you need to do now, and periodically for the rest of your married life, is to come up with new ways to be romantic as well as new ways to have sex. For women, the romance starts in the morning before you go to work: a lingering kiss goodbye, a whispered comment about how she looks/smells/moves, or telling her you're going to miss her that day, will start her mind rolling and her juices flowing. She'll be mad for your return in the afternoon and all it took was a little romance. Write her a poetic note and leave it where she'll find it during the day - a cutlery drawer in the kitchen - on the mirror in the bathroom (you get the idea). All those little things are important.
As for the sex itself, break it up. During intercourse pull out to go into more foreplay, repeating this until neither of your can stand it any longer. Or you can use only the head of your penis to enter her until you come. Or you can hand the whole act over to her, letting her be the aggressor, so to speak, so she may do as she pleases to you.
It's not only necessary, pwrtrp, it's fun!
As for that longed-for look of pain on her face, it may have turned you on when you were a kid but by now you should recognize that it was not exactly what she longed for.
Pecker
If Pandora hadn't been curious, there'd never have been a famous quote about her box.