I do not know what you man by "without it affecting anything" but you can have multiple romances.
I bounced between Piper and Cait without any consequences. I brought Piper to where Cait lives, slept there and got the bonus from Piper and no complain from Cait. Go for it, cheater!
Yep, you won't find yourself chained to the bed...
It is nice to know that women in the future are so open minded about relationships.