Pay question

Been barbering 20 yrs now-just recently took a job at a 4 yr old barbershop ran by a cop(go figure).He was paying salary(10.00 hour) I told him I wont take the job unless its 50/50.He agreed.I worked there 2 full wks and last night(in front of other staff)he tells me he cant pay me 50% that hes dropping it to 40%.He told me I had the highest # out of all the people who have ever worked there,I work alone 1 day for 10 hours so you have to hustle.Hes down to 2 workers (3 alltogether)due to high turnover.What do I do?He should have talked to me first before dropping the bomb.He tells me in front of the mgr and another girl that I made more $ than the mgr(who gets salary),She works very slow.I dont want to lose this job as its close to home and busy but now he's gotten under my skin and I feel like he let the wind out of my sails.I had reservations about working for someone whos not in the biz,hes clueless.Any advice? I pay for daycare too for 2 kids and now I will make alot less $.Hes thinking that he could have paid me 90.00 for the day(9 hrs)rather than 150.00, because I did 300 in sales that day,and pocket the rest.He doesnt understand that its standard to get 50/50 and I will make him more money in the long run.Im thinking of telling him I will settle for 40 then in 3 mo it needs to be 50 or I walk.I have the most experience out of the other 2 girls and neither do flat tops.Go figure.Im just really upset over the whole thing.