I agree with BigBart. Whilst it may seem selfish on my part, when I am breeding a willing ass, it's my orgasm that counts. And I am sure that most bottoms would prefer it if the Top shot his load inside their asses first.
I actually don't need to cum every time I get fucked. More important to me is that the top will cum and breed me. That's satisfies me equally and possibly more than to cum myself. Once I have a good raw cock inside me it like I am cumming. Need no more than that.