Trinity Love Interests:
Supes: Lois Lane, Lana Lang, Lori Lemaris, Lee Lambert (not yet, but probably), Wondy
Wondy: Steve Trevor, Tom Tressor, Trevor Barnes, Io (amazon blacksmith, mostly hinted at), Supes, Bats, Etta Candy (okay, hasn't happened, but it should!)
Bats: Catwoman, Jezebel Jet, Vicky Vale, Talia Al Ghul, tons of other miscellaneous women I can't be bothered to name or learn about, Wondy
Of course, Supes is the only one to have been able to maintain a relationship for a significant amount of time. Wonder Woman writers have never been able to settle on a "one true love interest" for her. It's Steve by default, as that was her creator's intention and he's got the 77 show to back him up. But DC until very recently hasn't given a fuck about Steve, and even then, he's been turned into a creepy douche in the comics and Diana broke up with him without us ever seeing them really be together on page. As for Bats, most of his writers agree he's not stable enough to be in a healthy relationship for long. Even with the Wonder Woman thing, most say they see it as a fling at best.