C'mon guys.........there is nothing wrong with an unresolved triangular love....we just need to hammer SK for being so indecisive, that's all!!!
And let's not speculate what is NOT shown regarding Alto and Sheryl, it's just a gimmick by SK and co. to tease our imagination. Whether they did OR not, is really really open to debate. However, I tend to believe that it is impossible since she is infected.