Modification of Custody: Summer Visitation

My question involves a child custody case from the State of: Texas. The ex husband has never did his summer visitation since our divorce in 2013. I never mentioned it and just kept right along with him doing alternating weekends during the summer. Now that he is remarried for about a month now, I received a text from him on April 30th saying that this summer he wants 30 days. I asked him why now and reminded him that he has never done this before. He stated the past is irrelevant and that he wants to spend more time with his girl. Mind you during the past years he has skip more weekends that I can count and has called off his two hour visitation during the week. But now he wants to spend more time. Our daughter has never spent more than two nights with him or away from me. My question is has a enough time past of him not utilizing his time in the summer that it would no longer be in the best interest of the child to go and to just keep the schedule that has been followed the last 3-4 years? What are my legal rights in this? The law seems very one sided. Meaning the father can cancel and not show but when he decides he wants to then I am forced to do so. Our daughter is now 7 and in camps and cheer during summer because I assumed that we would do what we've been doing since our divorce and just keep alternating weekends. I'm not trying to take his time but he really shouldnt be able to just change with the wind on when he chooses to use his visitation rights. Looking for advice in the matter. Thanks

Modification of Custody: Summer Visitation