In ME3, you can romance anyone, regardless of your prior romantic decisions. If you romance someone in ME1 and another in ME2, both will inquire about the other individual, at which point you may either break up with them or string them along even more. You may "like" numerous persons here. There is no consequence to this action beyond some cosmetic changes to their character page. The only person you cannot romance more than once is Anderson Shaw. If you do so, he will complain about his girlfriend/wife being flirtatious with others and move on. However, if you kill him, then you can romance whoever you want multiple times. In addition, you can also fall in love with aliens, robots, and humans all at once! All relationships are equal in terms of how they affect your standing with the Alliance or the Salarian Empire. If you choose to marry one of them, you can divorce them anytime after you wake up from your mission sleep mode. Finally, remember that you can like someone without kissing them first. This method is useful for quickly gaining respect from powerful individuals or for simply trying something new. Have fun romancing everyone you can!