Blended relationship (Oldest struggling)

My boyfriend and I came together with two children from our previous relationships. I have an almost one year old and he has a four year old. We’ve been together for a while now and with similar situations, we are in he process looking for a place to call our own with the exciting future possibilities of buying a home; everyone knows talking about the future can be exciting! 🙂

We try to get the kids together as often as possible. I’m a 9-5 full time employed assistant teacher where my daughter is with her dad Thurs-Saturday and Thurs-Sunday biweekly. My boyfriends son is with him on his off weeks; he works 8 on 6 off, and every weekend. But with me not having my daughter around the same time sometimes it gets hard to plan a fun family day. But when we do and get them out it’s a blast!

When I come over with my daughter, although his son takes a while to warm up when she’s here, after a while he can be nice and will smile and try to play; we’re working on playing nicely. But sometimes he’ll make it known he doesn’t want the “baby” here etc.

What can we do to make this a positive transition for his son? We know like everything with children, it’ll take time.