Help?

My boyfriend is very sensitive, but also very tough depending on the situation. He struggles with clinical depression, anxiety, and ptsd. He has gone through the worst shit and came out alive.

Anyway, we've been together for 4 years and our relationship has been kinky from the start. Since October though his testosterone has really plunged and when we do have sex it's super vanilla and quick. Don't get me wrong it still feels good, but it's just not doing it for me.

I love him and sex isn't everything for me, our relationship and sex life has felt like a married Christian couple that has been together for 20 years and I don't know how to talk to him about this