To me, and just IMO, I don't see any logic that weighs suicide as more likely than foul play that resulted in homicide. In fact, I believe that the evidence and circumstances weigh much more heavily toward foul play. As far a Tom reportedly having a lot of things "going on", such feelings are prevalent to some degree in virtually all "late" teens. Youngsters around the age of 17-18 are, for the first time in their short lives, are suddenly facing some "facts of life" that concerns them. They have been raised, protected, coddled, defended, provided for, and guided by their parents, teachers, and coaches. They are not used to having the weight of important life decisions on their shoulders, so some degree of uncertainty and anxiety arises. Regardless of how each one handles that new realization, they all have a lot "going on". It's a normal part of maturing.
Penny Meek and family want nothing more than the truth about what happened to Tom, regardless of what that truth is. They are honest and caring people who are striving to learn answers; Exactly as I and many others would be doing if in the same situation. I understand Lewis' frustration regarding the rumors and comments about him, but he brought much of that on himself by his own conduct. Lewis' tone and comments about Penny Meek speaks volumes about him.
I have posted earlier regarding some of my reasons that I believe point logically and heavily toward foul play, so I won't repost at this time.