You were right! A week ago I noticed the outer segments of the first bud started separating and now today it is starting to look like flower

I think it is a big groggy though, but hopefully it will open further within the next few days (and hopefully the other buds will follow the example).
A break-through, it's the first time in many years that the bud has opened. Thanks everyone for the advice, I think it helped. I spray the plant now several times a day and I've added some fertilizer when watering. I'm still planning to put them in a glass container. What should I do with the dying leaf, cut it off or let nature take it's time?