His ex wife - past problems affecting things now

Hi, I don't know if anyone can help me this is troubling me a bit. I am in a new relationship of 4 months with an older man 18 years older than me. He is divorced 10 years ago but was married for 14 years to a sociopathic sadistic golddigger that took everything left him on the street homeless and caused him to have a nervous breakdown. She lied to him all the way through as she was ciphoning off all his earnings each month and he didn't even know, then she even was getting benefits as a single parent so fraud too and never got caught. Basically, he told me it did his head in as when they had sex she would always come first. I said wtf really? I just couldn't understand how she hated him, was doing him over but having great sex it just doesn't make sense. Anyway, he is a bit gullible and I said look, she was faking it babe to keep you hooked in. Any woman can fake it you can't tell the difference. Anyway, the problem is when it comes to our sex life he always wants now me to 'come first' and I feel it's sort of a habit he got from when he was with his ex wife. It confuses me and puts me under pressure as I find it difficult anyway, haven't been in a relationship for years, let alone be the first one! Just wondering if anyone can shed light on this as it is really getting me down now.