How often should a father see his children,when you're engaged to be married & planning your future together?

My fiancee has 3 children, the youngest 17 and the oldest 19. I get on very well with them and have spent a lot of quality time with them. My partner has them every other weekend, Fri-Sun and every Wednesday evening. The problem is, he has to go back home to do this, which is a long way from me and I can't always go with him, due to responsibilities I have here. This means we are apart at these times, which I find difficult, as we shouldn't have to be apart. Because of this, I have decided to sell my home and move to his neck of the woods, but because of the way the market is at the moment, it's proving very difficult! I find that I am sacrificing so much and fitting in with his plans mainly and yet, he isn't having to sacrifice anything really. Am I expecting too much for him not to have the children so often and am I being selfish? I have 2 children that are independent now, and realise it's what I have to do, even though they are sad that I'm moving away and won't be so close to them. My partner and I love each other very much and are aware of the problems this causes every now and again. I need an outsiders point of view on this, to enable me to put things into perspective. Please help. Thank you.