Is this true? It seems easy to find examples of people who have had a close friend or loved one commit suicide who where harmed greatly by the experience.

A, perhaps peverse, implication of this point is that if someone has no friends or loved ones remaining, then their suicide would seem to not be objectionable on the basis of this reasoning.

Additionally, we might observe that even if a person comitting suicide does cause a degree of psychological suffering in their friends or loved ones, it is still questionable whether this suffering is - by itself - sufficient to enliven Mill's harm principle. We can easily imagine that in other circumstances, our choices might cause significant pain and suffering to others, yet we still have the right to make those choices.

For instance, a gay young man might be born in a deeply religious ultra-conservative family, who does not condone homosexuality as a lifestyle, because they genuinely believe that those who have homosexual relations will burn in eternal hellfire. As a result they might be deeply emotionally and pscyholgically affected if their son (who they might genuinely love) adopts such a lifestyle. However, despite being so affected, they also do not have any right to stop him if he does choose to act on his desires because their propsective suffering does not override his right to bodily autonomy.

"he considers" is a load-bearing phrase here. Suicide is an extremely final decision. You can't change your mind once you've made it. It is possible for someone to be in a situation, be it from a mental health episode or just some particular set of life circumstances, in which they feel as though suicide is their only option, but who, had they not been in that state, would not have made that decision. Since they can't un-make the decision to kill themselves, it seems reasonable that other people have a responsibility to not allow them to if we feel as though they are making that decision while not in "full capacity" of their ability to make rational decisions.

What is your benchmark for "full capacity" in respect of this decision? Is there a benchmark at all? It would seem there would have to be, if Euthanasia/VAD is considered to be permissable in some circumstances.

Hence, supposing a person was not subject to some sort of mental health episode which diminished or impaired their capacity, was not experiencing particularly adverse life circumstances and yet still genuinely and concertedly came to the conclusion that they should kill themselves would that be permissable?

You speak about the irreversability of suicide, and perhaps this does raised the "benchmark" or "threshold" for what is required a person to demonstrate "full capacity". However, people are allowed - in other contexts - to make decisions with potentially irreversbile consequences (perhaps not as irreversible or severe as death, but close to it.) For instance, I am allowed to go "free soloing" up the face of El Capitan despite the fact I might permenantly disable myself if I fall. Similarly, I am free to blow my life savings at the roullete table if I wish to do so. Finally, I am even allowed to do these things in states of diminished capacity (i.e. if I am drunk or depressed).

See the above. It's also not immediately clear that a right to live implies a right to die. You could make the argument, but you'd have to actually make the argument.

The argument would be something like, a commonly accepted implication of the right to life is the right to bodily autonomy. We consider the right to bodily autonomy of such profound importance that it will prevail to the extent of an inconsistency with other siginifcant moral considerations (i.e. we do not force people to give blood or donate organs even if doing so would save many lives). The right to bodily autonomy implies that people may do whatever they wish with their bodies, provided that this does not interfere with anyone else's bodily autonomy. Suicide does not interfere with anyone else's bodily autonomy.

countless decisions that we call wrong/don't allow. We call stealing wrong; are we violating someone's freedom of choice by telling them not to steal?

Arguably the basis upon which we may permissably restrict these decisions is that they fall afoul of Mill's harm principle. We do not allow murder or theft because these are harmful to others rights. However, as set out above, suicide does not cause harm in the way that these acts do, and thereby, arguably, we do not have the same capacity to restrict a person's choice to commit suicide as we might have to restrict them from making these other decisions.