Well they are human. I think it's not unreasonable that at least a decent portion would want the D.
Of course they wouldn't settle for low tier D, but there are plenty of valerous and faithful men in the Imperium. War Hero's and Saints, fellow Schola graduates. I don't think it would be unreasonable to say there would be men individual sisters could consider worthy equals, or who they could exhibit interest in. Commisars, regimental champions, particularly hard core crusaders, a bad ass ministorum priest maybe.
I don't deny that there are probably some lesbian proclivities for a large number of Sisters, but it's a big galaxy. I simply can't believe all sisters are carpet munchers, it doesn't add up.
That ia just my opinion, bit all we have to go on is opinion, it's not like gw has come out and said one way or the other what cannon sister sexuality is like. We do in fact have some instances in bl where sisters had male lovers, but I won't point to them as evidence.
Ultimately it comes down to ones own interpretation and preferences and there is no real way to prove anyone else wrong.