Its true that he's got the length of history with her that the time frame would work out for him to be the father. There's never been any indication of them having a romantic or sexual aspect to their relationship though. In one issue, Mandrill referred to Nekra as his "sister".
I guess that doesn't necessarily rule out them having briefly had a physical relationship years ago, and then ending up in a more sibling-like relationship after the relationship turned platonic.
The Hood - he has/had a girlfriend named Sara who is the mother of his child. He used to regularly frequent a prostitute named Gro. He and Madame Masque were an item for a while.
The Fenris twins!
Andrea Strucker has been reportedly been with a lot of men, although I'm not sure many of them have been identified as of yet. We know she's slept with Gambit and with Citizen V (John Watkins III). Possibly Helmut Zemo when he was possessing Watkins' body. I'm not sure if any others have been identified.
Andreas Strucker was apparently involved with the new Whiplash and Backlash from the Thunderbolts Army, in BDSM sex clubs before they decided to become super villains. He also sexually served the Purple Man while he was under Killgrave's control, but that certainly wasn't a consensual relationship. I don't think we know of anyone else for him yet, although like his sister he is implied to be a slut.
I suspect the both of them will soon be sleeping with Shinobi Shaw in MARAUDERS, but we'll see.
The two of them have also been frequently speculated to have an incestuous relationship, but that was apparently refuted in THUNDERBOLTS when the siblings were alone and talking about the "ugly rumours" about them and how people misinterpret their relationship. Of course, the two of them make it very easy to misinterpret...Andrea was naked and having her brother brush her hair at the time. They may not actually be sleeping together, but they are creepy in their closeness.
The Fenris Twins are definitely swingers. I would like to see more of them with Helmut Zemo.
Amazing Spider-Man #84 May 1970
"The Kingpin Strikes Back!"
Peter could use the $5,000 reward, so Spidey sets out to capture The Schemer;
He eventually finds him in his fancy car but keeps falling off it;
Schemer arrives at the Kingpin's mansion and confronts him;
Vanessa intervenes. Spider-Man has followed Schemer, breaks in,
and has a brief tiff with Kingpin before both realize that Schemer - and Vanessa - have vanished.
Script by Stan Lee, pencils by John Romita (layouts) and John Buscema (finishes), inks by Jim Mooney