I too got a distinct feeling that the "Join" option was the "happy ending", even more so than "Live". I'm sure this wasn't the developer's message and that there's a deeper meaning. Perhaps they're portraying what suicide can feel like to a person who is grieving and actively suicidal, but I can see how it can trigger people in similar situations to have thoughts of SU.
I'm sorry this has caused your boyfriend to have suicidal thoughts. My advice is to seek professional help if you are worried. I know this is a late reply, but talk to your doctor, or a local suicide prevention/psychiatric organisation. You'll get more concrete advice from them.