Child with different sleep environments, won't sleep in own bed. What should I do?

[angel_gurl_13_2001]

I live with my boyfriend and his 7-year-old son. Right now, for the summer, his son stays with us half the week, and then stays with his mom and grandma the other half. When he sleeps at his mom's, he has his own room but shares a bed with his brother. When he sleeps at his Grandma's, he shares a room with his aunt and sleeps with her. When he stays with us, he has his own room with his own bed. His father works at night, but when he does not work, he lets his son stay up however long and lets him sleep anywhere. I do not approve of this since he has his own bed and own room to sleep in. When his Dad is at work, I have him sleep in his own bed. But, every night, he goes to sleep, he'll wake up in the middle of the night and come sleep on the floor next to my bed or will sleep in the living room. How can I get him to sleep in how own bed? What should I tell his Dad? I have a routine bedtime of 10PM during the summer, but Dad does not feel this is necessary. What should I do? Thank you.
I have been in this relationship for over three years and support my boyfriend and his son in many ways... this is why I feel I have a right to ask for some advice regarding this particular issue. Thank you.