OP I really feel for you. It's so hard.
I can share my experience of my darling brother being sectioned. I don't want to scare you at all, but I'll be honest about it.
The first couple of times, it was for a maximum of 28 days. The third time, unbeknownst to my dad, he inadvertently got coerced into an agreement where they could keep him indefinitely.
This turned out to be terrifying, because the first facility he was taken to was a 3hr drive from our home and it was horrendous. The staff didn't seem to care at all about the patients (obviously they were low paid and doing a hard job etc, but honestly, they didn't care). My brother swore he was being abused and sedated in there. He was paranoid, so we couldn't tell if this was true, but his behaviour seemed really off when we could communicate with him/see him and he was slurring his speech and had other symptoms which we thought seemed strange.. sedation was not supposed to be happening in his case. The medication he was being given didn't seem to be working for him, he wasn't getting better.
Staff often prevented us from visiting/talking to him and controlled his access to his phone. My dad sat in his car feeling absolutely desperate outside that place for hours, unable to see or speak with my brother. At one point my brother was so desperate that he escaped by jumping the fences, but was located and taken back.
We advocated like crazy and eventually got him moved to a different facility. He did improve there and was much better when he came out.
So if it's the first time, I would just say - try to check the conditions of the section and make sure you understand when he can come out again, try and get a facility near you if possible so you can visit easily, ask how much access the patient will have to their phone, how they charge it (not allowed cables for obvs reasons), are you allowed to take care packages with treats he likes or will they restrict what you can take in for him. Ask how his doctors will communicate with you and how often, who will be your point person. Try and check reviews of the place he will be going to, see if you can find out who the doctors are there, do they have good reputations, etc. (Don't necessarily believe a nice shiny website talking about how great it is!!). You may not be able to do all this in advance, but it's worth a try.
Finally, I just wanted to say that you need to remember you are not abandoning him, you love him so much and want the best outcome for him which honestly may require some time in hospital. It is not your fault he is ill. So much of this is out of your control. Whatever decision you make, you will be making it with his best interests at heart and you don't need to feel guilty about it, because you only want the best for him. Sometimes a medical facility really is the best place for somebody who is a risk to themselves. And there are some very good ones with great staff and doctors.
As a pp said, you also need a break from this if medication at home is not helping. You are worthy of peace and rest, and you cannot battle your sons demons alone. You need help from professionals. If you can also get some counselling, that might also be good?
Hope this is helpful. Sending love and wishing you and your son all the best xx