Personally, I see both sides of the issue.

One one hand, no one should be restricted from serving our country if it is their wish - unless they have a physical reason they cannot do so.

On the other hand, if there are sexual relations going on within a unit, a soldier (man, woman, gay, lesbian, straight, etc) might not have his/her head completely in the battle if he or she is concerned with the safety of a loved one that is fighting side-by-side with said soldier. I believe this more than anything is the concern of the government. However, that door has already been opened by allowing women to serve in combat, so because that line has already been crossed, I feel that this specific argument is moot. If the argument is used that being forced into combat with someone who's sexual orientation makes said soldier uncomfortable, then the government MIGHT win that case, because there are enough "touchy-feely" people out there to stand behind this issue. I believe though that the military (whichever armed force the soldier serves in) instills enough maturity and bolsters patriotism to the point it overrides any misgivings about another person's sexuality.