It all gets down to intent and frequency. A YM/YW that has messed up just once and then came forward, or at least stopped, tried to make things right, and then came forward will be treated better than those that have a long-term sexual relationship with one partner or with multiple partners. That type of behavior implies more than being out late one night and being stupid, it implies a level of rebelliousness that is hard to overlook. That doesn't mean that they cannot be forgiven, and indeed can and will be if they come forward and repent, but since they must go out and teach the law of chastity to those seeking baptism, as well as obedience to the words of the prophets, it may be hard for them to do so.
As for the homosexual activity, the same standard applies, except if any activity occurred in the late teen years, then there is a different issue altogether, and putting the person in a situation where they have to be around their companion 100% of the time just seems a tad unfair if they are struggling with SSA.
That would not be difficult to express. I found most helpful to me was going to my knees thanking my HF for life, for experience, for my family, and then directly asking him to go before my face, to be on my right hand, to be on my left hand, and his spirit in my heart, and his angels round about me to bear me up. --Thomas S. Monson, Feb 4 2008 News conference upon becoming President of the LDS church.
Hard work won’t kill you, but why take the chance??
---Motto of the Democrat Party