I can't initiate sex

I want to and try to all the time, which works but when I do, he can't cum. We have sex for a while but then he goes soft. It's frusterating because I don't always want it when he does. But thw only time we can both be pleasured is when he initiates. Morning sex or anytime other than bedtime is a wash and doesn't work. We can't be spontaneous or he won't finish. I am trying to be super sympathetic but I'm honestly getting frustrated. We've been together 3 years and this has always been an issue. I wouldn't want him to get frustrated with me if it was the other way around but I hate having sex on a schedule. Thoughts?