I strongly believe that if you've had a conversation with him about you feeling uncomfortable with him using only fans to watch other naked girls online when you two are in a relationship, then he is the problem. You are worthy of love and if he is failing to make you feel that way (physically and emotionally), and instead focusing his attention on other girls online then you may just have to question his fidelity and commitment to you. If he sounds agitated or tries to insinuate that you are being insecure even after another conversation then know this he is not worth your stress and sadness. If you feel worried that he is going to become angry or avoid speaking to you by brining this up then it is time to cut off ties with him, it may be difficult but will be better in the long run.