You might want to read a bit about “emotional blackmail”. Basically, emotional blackmail involves people giving or threatening to give emotional pain if you don’t do what they want you to do.

There is a difference between giving support to a friend and becoming their de facto therapist with soft boundaries. And also it is unhealthy for him to rely on you indefinitely rather than to actually address his problems.

It sounds like you have a kind and loving heart. My suggestion is that you do more to include yourself in that kindness and love. You don’t have to endure emotional pain indefinitely in order to protect him. I suggest therefore that you have some sort of limit in mind, how long you are going to put up with him not being convinced, not seeking professional help. Without that, you are in danger of becoming his emotional prisoner.