Batman needs to sleep with the whole League because sex is the only way for him to relax and let go and distract him form everything else. And its the kind of care he can, at some point, only get from fellow heroes. As his career as Batman progresses, his body collects scars, and suddenly Bruce Wayne can't just let himself have casual sex.
Call it sex addiction or dependency, but those few weeks between him realising his skin is too damaged to be frivolously shown for strangers to admire, and him finally breaking his own rule and seeking a partner within the group of his coworkers, was a torture.
Yeah you can have sex in clothes. You can just pull your pants a bit down, do your thing, and that's it. But this is not the kind of sex that provides Bruce good relief. He is attentive lover. He needs to be close and intimate. He gets sooo involved. It's a problem, because those few hours in bed are pretty much enough for anyone to fall in love with a man they already deeply admire.