It you have thought it through and really are intent on ctb, don't tell anyone, not even your SO or live-in partner. Nothing good is going to come from doing that. Depending on how they react, you may find yourself institutionalized, if they decide to seek help for you. At best, they can, at least, take steps to make it difficult for you to ctb, or tell others, including your family, of your plans. Nope, ctb is a very personal decision and needs to kept at that level, if, indeed, you are serious about it. People who are on the fence oftentimes tell others. But, it is more of a cry for help. If you want help, by all means tell someone. If not, keep it to yourself. You can still tell your SO, or live-in, how much you care for them and how much it means that they are in your life, and how glad you are that they are in your life. Leave them a note or letter telling them how grateful you were to have known them and how much it has meant to you. Make it clear that your ctb had absolutely nothing to do with them.