How do I get over the guilt of wanting to put my mom in an AL facility. I can't do this anymore.

I agree, placement of mom benefits both of you

I agree with the advice that everyone has given: you have the right to live your own life, and you also have a responsibility to take care of your health and to prioritise your marriage. It will do your mother no favours if you drive yourself to an early grave. So no. You are NOT wrong, not about the decisions you need to take.

Just... can you stop blaming her, please? She's 89 years old and she has dementia. You're expecting her to adjust to the presence of a brand new husband in your life, expecting her to be considerate in her demands on you, and in a way expecting her to absolve you of the guilt you feel about making practical arrangements for her care. It's not reasonable.

Why aren't any of the other relatives interested?

No, of course you are not wrong. You have a right to your own life and you should have it, and in fact you are obligated in my opinion to take care of yourself first, and your primary relationship with your husband second. You should do the best you can for a parent. Do allow yourself now to find her the best placement you can given the assets she has, and have her enter Assisted Living. She may surprise you, after adjustment, by liking it a whole lot; but that beside the point, you are obligated to make a happy life out of the life she gave you.
Remember that old Eagle story of mine? The one where the deluge has arrived and the father eagle is attempting to save his two eaglets. He takes the first from the next and carries it across the raging waters; he asks the chick "And when I am old and weak, will you like save ME from the floods?" The chick answers, "Oh, yes, father. I promise that I will." The Eagle immediately drops this chick into the waters where it quickly perishes. He returns to the nest and rescues the remaining eaglet in his talons and takes off. He asks the same question of the chick, and this chick replies "No, father, I am so sorry but I will not be able to save you. But I promise you that I will use every ounce of my strength to save my own chicks".
This is the way of it. Live your life. It is the only one you have. You are not experiencing guilt. Guilt belongs to felons and evil doers who realize the harm they have done and pray for redemption. What you are experiencing is more like grief. Grief that you are not a Saint, but merely a human with human needs and human limitations. Saints are not good jobs to apply for; they are filled with arrows, killed, and prayed to for eternity to fix everything for us.
Hugs out to you. This won't be easy, but it is the right thing to do, and you will have more loving support to give.

The body tells us what we sometimes can’t see. I am dealing with cancer now and no doubt in my mind that it is in some part due to stressful family issues. Working on boundaries and saying no which lately I’m getting pretty good at. You deserve some peace. Your Mom will be fine at ALF.

My folks have lived in a wonderful ALF since 2014; after dad passed away in 2015, I moved my mother to a smaller room in the same ALF where she still lives to this day, just in the Memory Care bldg now. Since her dementia has progressed, she feels like she SHOULD be living with me and my husband, but that's not going to happen because she has WAY too many issues to be dealt with at home, especially for an only child such as I am.

My point is this: You are doing nothing wrong by placing your mom into an ALF. She will get to hang around with a bunch of people her own age and do activities, crafts, eat 3 hot meals and 3 snacks a day, and all sorts of other things. You can take YOUR life back and try to get YOUR health back under control. We often read the stats about care givers dying BEFORE their elders because of reasons such as you've mentioned. YOUR health is falling apart and still you're worrying about your mother.

She will be perfectly fine in an ALF, as my mother is, rest assured.

Wishing you the best of luck moving forward with this decision and feeling GOOD about it!

When you have done all you can do ........

So your guilt is what- abandoning caregiving, promising not to place her in a facility, not having the energy, strength or desire to continue caregiving?

Guilt is reserved for someone who has commited a wrongdoing and regrets it. But you want to do the right thing and still feel guilty.

So what would be the right thing to do? Your mom has dementia and you have health issues of your own. In the present situation you will both continue to decline. Your mom's declining is inevitable, but your's isn't. You are not wrong in wanting to take care of yourself- you must. Dementia can also damage relationships. You're newly married so protect that relationship by moving your mom to a care facility. Sure they want her SS check and her pension, they don't provide free room and board. When you convince yourself that your doing the right thing, your grief will be replaced with relief and freedom.

I wish you well.

There is no medication for guilt, but there is for depression. See you doctor.