Tammy, I hate to also be one who feels you shouldn't visit, but I do sadly agree with the others.
I do hope that your difficult child is having a wake up call moment in jail with nothing but time to think. I must say that indeed he has a talent for writing which if put to good use might be a tool that is a healthy means of expression for himself. Perhaps a journal to write his thoughts and fears and guilt etc. But I also feel compelled to tell you, since we've known each other here for so many years, that I do believe this is a "pity party". He probably DOES feel this way, but he knows (and he knows that you and others know) that he has brought this on himself. He has not been thrown to a deserted island to fend for himself for life. He's sitting in jail for a violent outburst that put his partner and his beautiful child at risk, which was caused by his own mental health neglect, addictions and anger issues. He has a lot of work to do to be healthy and in a frame of mind that will stop this "woe is me, I want attention, where's my letters, I screwed up but why should I then be unloved" thing he's going on about. That poem screams manipulation to me. No part of him feels he is unloved, in fact he's possibly had so much love that it has blinded him to just how horrible the consequences are to his loved ones when he continues to make these choices for himself and his life. It is time for him to pee and get off that pot, pull up his big girl pants, take responsability in a ADULT fashion (I was WRONG, I MUST do better/different, I WILL regain trust and be worthy of it. FULL STOP. *no blame but self blame*).
I think you do not only him but yourself a huge injustice if you go visit. I wouldn't even send daily letters, although I would send one once or perhaps twice a week. I wouldn't at ALL touch on this topic in my letter, no reference to anything to give attention to pity trips, as honestly? That poem was MEANT to guilt you, to picture your beloved son sitting in a cage, awake middle of the night from a bad dream that something happened to one of you, staring out at a highway wanting freedom. He is good, I'll give him that! He poured it on quite thick. And as for his reference to sobriety, you know that forced sobriety due to incarceration is NO demonstration on what choices he will make when he does get his "freedom". But past behavior is a good indicator, this is far from the first time he's played the I am sober now card, I need you all, thing.
I know you raised your kids right Tammy and I know how much you love your children. Trust me when I say, he knows you love him. He also knows you love him to a point you have faith in him. That is NOT a bad thing, he should have his own mother have faith in him. That however does NOT negate his need to prove with his actions over time that he IS going to change.
I recommend you take care of yourself and send the odd letter, heartfelt but not at all along the tone he is setting in his letters. You've been through a lot with your sons and this isn't a completed story yet either. Take this time to regroup yourself and let him be the adult man/father/spouse he is meant to be. He and only he can get himself to a place where he is deserving of trust. At this stage of his life, he does not need mom/dad/siblings to pity him, he needs a loving family who are there when he gets his act together and he needs a family capable of realizing he is no child gone wayward, he's a grown man with responsabilities that he needs to focus on. His focus should be on being the man he needs to be for that child, for himself. He'll know you're out there rooting for him, he's always known it. Perhaps now is the time to stand your ground and let him see that the role you have played in his life is now changed, based on his age, his choices etc. It's unnatural with non difficult child's to be this involved in our childrens bad decisions and consequences. I think at this point with your difficult child, it is past time to let him deal with this on his own. Literally, on his own.
Whatever decision you make, you know I've always supported you and admired you. I hope my post doesn't offend you as I don't intend it to. I just have known how much you've done to try to guide these man/children of yours and I think now is the time for them to put the lessons you've taught them to good use by taking control of their own lives and actions.