Does that mean if the female is open to receive babies but the male pulls out, or wears a condom, the sin is his?
It could be argued yes. However, many women who are open to life (including myself) find the idea of sex with ABC repulsive. If my husband ever started talking about condoms or vasectomies, I might start talking about separate bedrooms.

Fortunately, we both agree that NFP is best for us.
We have been married seven years, and in that time we have used two different methods of NFP, and we like both. As a woman, I wish I had learned all this stuff about my body when I was 12. It has helped me take much better care of myself, and thanks to a doctor trained to interpret my charts, has made it possible to fix reproductive health problems that have plagued me since my teens (I am now in my 30s)
As a wife, I like that NFP helps my husband to respect my fertility and keeps him from taking sex for granted (whether we are avoiding or trying to conceive). Charting also empowers him to be a better husband–having hard data showing what my hormones are doing, how they affect my moods and my emotional needs allows him to be a more sensitive partner. . It has made communication within our marriage easier
Alas, our attempts to conceive have not been successful so far, but that leads me to another benefit of practicing NFP with a heart open to life. That is, you learn to keep an open mind about the future, and the possibility that plans may have to change. If I had bought into the illusion of total control that ABC and artificial reproductive technologies offer, I think the pain of infertility would have driven both of us out of our minds long ago. NFP helped us develop an appreciation for and acceptance of fertility (to whatever extent we may or may not have it), a desire to understand and care for our bodies, and an attitude of acceptance toward the reality of how our bodies are working at a given time
Even if we cease to use the charting to guide the timing of our marital embrace, we will continue to chart as long as my cycles last. It has been challenging at times, but that challenge has been good for our souls and our marriage.
OP, I hope your girlfriend will come to see this. If she is unable to, you may be happier waiting to marry until you find someone who does.