AIO I Dog walked/sat for 2 years for this to happen..

After 2 years of loyal service while in school I thought I had the perfect gig. $400 a week to walk 2 German Shepard and occasionally house sit for an older married couple. They wanted the dogs walked at between 5-7am at least 3 days a week, in the last couple of months they randomly would request more days or immediate service which I accommodated as it was early enough to not be an issue. Recently I stayed at their house for 16 days straight with the dogs because the money was good… they asked me to stay again this weekend over a month ago but I just started a new job which I worked hard to get and this was their response to not being flexible ONE TIME.. I never said I couldn’t do it I just said I also had work the same days so I wouldn’t be there 24/7 but could still do the job and this was the wife’s response!! I’m lost and baffled that after so much dedication and loyalty I was met with this response so please analyze and let me know if I’m the A Hole