Matters of the heart can be incredibly stressful, I can't imagine what you are going through.
It sounds like you have built a very strong, supportive friendship with this person and the romantic feelings you have developed have caused a lot of inner turmoil. Although I can't relate exactly, in my personal experience with unrequited love/strong feelings for someone, it can be incredibly challenging as you consider the 'what ifs'.
Firstly, I think it's absolutely great that you have been speaking to your psychologist about this - a great neutral party to help you cope with what you have been going through.
In my own experience I found it really helpful to write out different scenarios and the outcomes for example:
1) You confess your feelings, however you lose the friendship
2) You confess your feelings, the man's partner finds out and it causes conflict
3) You do not confess your feelings, learn the new 'normal' of your friendship
I know this must be an incredibly difficult situation for you, at the end of the day your mental health and wellbeing is the most important.
I hope that we can support you through this journey so please feel free to reach out!