husband cosleeps in SD room

I’m newly married for a year and my SD just turned 5 yrs old. He has 50/50 custody. So we have his 2 kids every other week. I’m struggling bad with him falling asleep in her room almost every night and not coming back to bed once she’s asleep. I’ve let him know it bothers me but he thinks she’s still little and I shouldn’t get upset by him loving his daughter. I also have 2 grown kids, and have experience with kids wanting a parent to sleep with but I never fell asleep all night long. Just waited till they were asleep then went back to my room. So every other week I’m alone at night. Should I just get over it or are my feelings valid?