May I ask how long you have been on Fluxotine?I am on Sertraline for anxiety and it has helped me overcome so much. I went through a phase of not being able to remember or concentrate. It's horrible but it will pass.
He might also benefit from reading MIND’s information on how he can help himself. https://www.mind.org.uk/information-support/types-of-mental-health-problems/suicidal-feelings/helping-yourself-now
If he feels that he may be an immediate danger to himself, please call 999 or go to his local hospital right away.
Due to you mentioning that he thinks suicide is one of his choices, we must offer the support that is available. It is clear that you are a very supportive mum and it's good that he feels comfortable to open up about how he feels to you.
I understand his situation is difficult as there is a child involved. I really do hope this settles