Consent: is it OK to go from No to Yes in one evening?

(X-posted from School for Scandal)

So, I am really lucky to have good health insurance and a great gynecologist. (I was seeing a GP before who was fucking useless.)My current gyno got me on continuous birth control on a low estrogen pill, as a person whose life used to be ruled by PMDD, this is one of the best things to ever happen to me.

So anyway, I visited her a few days ago for my checkup, and I told her about my plans to become a sex therapist. She told me about how she treats a lot of patients with sexual dysfunction and advises them to use vibrators (and referred me to her favorite vibrator shop). I love having a sex positive gyno (the first one I ever saw when I was a teen told me I shouldn't shave my pubic hair and that I needed to lose weight- I guess she was working at my high school's free clinic for a reason.)

I also told my Doctor about SlutWalk. She told me she treats a lot of women who have been dateraped and the advice she gives about consent is this:

"If you say no one evening, you need to stick to that no. You can say yes the next evening, but you need to be consistent with your consent, otherwise men think that if they push hard enough, they can turn a no into a yes."

I see her point (a similar technique is used to keep dogs from begging for scraps at a table) but if it's generally agreed that if you initially give consent and change your mind, you have a right to stop things without being judged. (I'm not talking about wishing you hadn't slept with someone the next day or retroactively changing your consent, I'm talking about actively communicating a change in consent at the actual moment.) So is it legit to say at the beginning of any evening, "I don't want to have sex tonight," and then after some heavy making out say, "I changed my mind, I do want to have sex tonight?" I think a mature dude should be able to handle this without assuming that he can turn every no into a yes. But is it, as my gyno claims, breeding messy boundaries? It certainly enforces the idea that women are responsible for preventing rape, rather than teaching men to roll with clearly communicated changes in consent without making assumptions.

I can think of one specific incident where I did this. It was on a second date with my previous boyfriend. We started making out and I told him I didn't want to go below the waist. The truth was, I did want to have sex with him but I set this boundary because I was looking for a relationship, not a hookup, and I wanted to take things slow. However, things got late, my train stopped running, and it was clear that I was going to sleep over, and I wanted to. So, I said "fuck it," and changed my consent (and clearly communicated this.) The next morning we talked about it over breakfast. "I did want to have sex with you, but I was afraid you would treat me weird the morning after if we did it so soon," I explained.

"Am I treating you weird now?" He asked, giving me a hug. And we did start a relationship, even though we had sex on the second date instead of the third, or fifth, or six months, or whatever society dictates as the appropriate time to have sex in the context of a relationship.

(An aside- anyone who casts you aside for having sex with them "too soon" is not worth being in a relationship with. Anyone you have to "manipulate" into a relationship, rules style, is probably not going to be a good partner. But it's probably a good idea to keep your expectations low in the beginning.)

So it was a weird situation because I initially said "No" out of fear of rejection, even though I wanted to say "Yes," and did change my consent over the course of an evening. I don't think this incident has made my ex into a date rapist, but I can see how with some less evolved dudes it might be problematic.

Very curious to hear what others think about this.