You could just try some honesty, you know. If your wife says no, then you can say to her, "I understand you don't want to have sex. It's cool. But please understand that I am frustrated with the situation, and it's going to take me a bit to get over my hurt. I'm not mad at you, I'm just feeling hurt."
In the same way she expects you to understand her right to say no, she also needs to understand your right to your feelings. Sometimes just being able to say it out loud... and maybe a few hugs... might help.
Also, tell her (at a time when sex isn't even on the table)... "honey, it would help me if when you said no, you might say... "no, not tonight, I'm feeling... x, y, z... but I'm willing to give it a go tomorrow night (or whenever night/day/time she is willing)... so that you aren't just left with an unknown. BUT. If she is going to give you a date/place/time, she needs to honor it. If not, then don't say it.
