Over the last decade my wife of 20 years has been involved in numerous affairs, mostly involving her work colleagues. She’s bipolar and uses this as her excuse.    
      I’ve turned a blind eye to this behavior for the sake of our family … until I found out about another affair.    
      I gave her non-negotiable conditions if she wanted to keep the marriage working. If not, the marriage is over and no guarantees. Our children are grown, so staying for the sake of the family is out of the question.    
      She’s not manic at this time, nor has she been in a while.I'm beginning to feel guilty about leaving because of her being bipolar. Or am I just being played? I’m not going to be a doormat anymore!
      - Burnt Out

There are two glaring needs here: the health of your marriage and your wife’s own mental health. Yet both are being sadly neglected.     
      She’s distracted herself with sexual affairs; you’ve unwittingly enabled her by accepting her excuse, without insisting on “treatment” for both of these ills in your household.    
      Her bipolar condition cannot be simply assessed as “manic’ or “not manic.” No matter how long she’s been diagnosed as bipolar, she requires ongoing monitoring and therapy by a specialist in her condition.      
      If she refuses to see her doctor in order to manage her situation through its more difficult manifestations, then she effectively gave up on the marriage long ago.     
      Despite that her pattern of affairs has persisted, your “non-negotiable” conditions, as an ultimatum should include her getting medical help; plus both of you getting help learning to deal with her bipolar episodes - and joint marriage therapy.

I live in a communal house as a student with a fellow student. He does things that are quite irksome, e.g. the worst is when he drinks straight out of the water pitcher, which we all use.      
      He also taste-tests off the wooden spoon while cooking food meant for the whole house, and has (absent-mindedly?) used my chap stick. He said he found it in his room, which he didn't.     
      I know that he lies because I’ve heard him do so to others, so I know that if I were to comment on his behaviour, he'd somehow excuse it, like he did with the chap stick.     
      I don't necessarily want to embarrass him or come across as the "disapproving woman-figure," but I get really bugged. What’s a tactful, diplomatic, yet effective response to his actions? Living arrangements cannot be changed at this time.
      - Sharing Germs

Instead of commenting on his behaviour – which does come across as disapproving and critical, whether from a female or male – try talking straight to this guy.     
      It’s much more respectful and gives him a chance to at least understand your point of view without having to defend himself. Something like, “Hey, did you know we all carry so many germs in our mouths that just using another’s spoon could pass on colds and viruses?”     
      You could also talk to others in the communal house and work up some “house rules” on group hygiene that don’t just pinpoint HIS behaviours.    
      Meanwhile, try NOT to get “really bugged” and try not to overreact. Communal living calls for some accommodations on your part, too.    
      By the way, there are few cooks who don’t occasionally taste-test from their cooking spoon. Fortunately, high heat usually kills off the germs. But if the cook is ill, he/she shouldn’t have his turn that day.

FEEDBACK Here’s a charming response to the January 9question from a graduate student who wanted to propose marriage and was concerned about ring costs:    
      Reader - “My then-boyfriend and I lived in a cramped little apartment and were saving up for a house. We were also talking about the future and about getting married.
      “He asked if I’d like a ring. I said I’d rather he spend the money on something we can enjoy together.    
      “When we bought a house a few months later, my husband paid to have the backyard fenced in so that my wonderful dog would not have to spend his senior days tied to a tree.       
      “The dog is very happy, so I am happy. I love my engagement fence because it’s a unique reminder of how much my husband appreciates my perspective on the world.”
      Answer - The key to this satisfying “engagement fence” purchase was communication.