I’d appreciate some advice on how to avoid things becoming repetitive.

I feel that sex with a woman I’ve been seeing for a year and a half has become rather predictable. We just repeat the same positions: woman-on-top, from behind, and missionary. Once with clitoral stimulation, once with G-spot stimulation, about five minutes on top, ten minutes thrusting from behind, then five minutes with her thighs over my shoulders at a faster pace, finishing in a predictable grand finale every time. I’m reasonably satisfied, but I worry about how she really feels about it. She does moan, writhe, and occasionally have contractions, but that may simply be part of putting on a performance, so it’s hard to say. She doesn’t like toys, trying new positions, or approaches that differ from our usual routine. I’m afraid she’ll get bored with me. I want to treat her well and make sure she’s satisfied. How long does it usually take for women to get bored with the same routine? At what point do they start wishing their partner would change the way he approaches them? Or do some women prefer to keep their own pattern of climaxing the same and not change things much?