User blog comment:AdmMiller/Who's pschyed up for ME3? (Romance options only)/@comment-743796-20100712010334

I think it would depend on the profile of the characters....

It's pretty much guaranteed that things will go very wrong if Shepard cheats on Ashley, especially with a non-human partner, due to her clear xenophobia towards them.

On the other hand if you cheated on Liara, she could more likely be sympathetic to it (considering she would live much longer than Shepard), or she could react violently (since her demeanor greatly changed as a result of tracking down the [SPOILER] Shadow Broker for the time that she did.