Changing visitation agreement

my ex has a dinner visit every wed from 6-8p. he has missed approx 12 out of 24 visits canceling bc he is “sick” usually with less than 4 hours notice.
Is there anything I can do? this is very upsetting to my son. Also, ex often threatens to take me to court to get 50/50 custody. We have had a custody agreement since March of 2008. Is this easy for him to do? He often threatens if I say no to something that’s not in our agreement. Thanks

You cannot force him to exercise his visitation. In order for your ex to change custody he would have to allege and prove that a substantial change in circumstances affecting the best interests of your son has occurred since the entry of the last order. His track record of missing visitation would not look good if he was to try and move forward and gain more time.

But is there anything I can do to get my wednesday nights back? my son has a developmental delay and his teacher is willing to write a letter about how this is unhealthy for him.

Not without filing your own motion to modify custody based on the alleged detrimental affect to the child.