I am suffering in a platonic marriage that is otherwise happy what do I do?

weve been together 15 yrs.married 10.we are in a very good marriage and never ever argue or yell. we are best friends.we are intimate about every 4-6wks or worse.this makes me miserable,he's ok with it.Ihave done all the"spice it up" stuff over the years.believe me I really have stretched and thought of all the typical and creative things to do.It is good for one night but it doesn't last.I'm lonely. he gets mad when I confront him and says I just want like its not so important considering every thing else is fine.We work long hours,so does everyone.we're tired so is everyone.I even start flirting with him all day(we have a biz together)and we make plans all day for that night.what we are going to do to each other,etc.the majority of the time he gets out of it when the time comes.doesn't go to bed till later, is tired now, etc.He's not likely having an affair cuz we are together all the time,so its not that.I ask him if hes attracted to me,he says yes. his plumbing works.what to do