I'm just disappointed

I've been with my boyfriend for 11 months but we were seeing each other for 4 months before we became official. so we have been seeing each other for 15 months. He has a son from a previous relationship and has joint custody. Well it just seems like every time we try and plan something, his ex is sick or has an excuse as to why he needs to come get their son and watch him. Don't get me wrong. I know he's a dad and his son is his responsibility. But we live in a small town where everyone knows everyone. When it was my birthday it was a big plan weeks in the making because it was my 21st and a big bash and an hour before she called him and was like I'm sick come get our son. Valentine's day around 4 pm. She called while because she had plans and we had to turn around and come back. We went away for a long weekend and the second day into it she called saying she was sick and unable to watch him. And today being new years <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">eve</a> (and the first new years <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">eve</a> he and I were going to be doing something) we made plans. Now just the way the visitation worked out he had his son last night and today up until noon when he would bring him back to his mom's. Well he called her around 11:30am this morning to let her know he was on his way. No answer. Went to her house thinking oh she's sleeping. No answer. So he tried calling some more but at a point he just took his son back home with him. 8 pm she finally picks up saying how she's sick and needs him to watch him. And our plans were to go downtown and do the whole skating and fireworks show. But yet again cancelled. I'm just disheartened because it happens all the time. By the way I might add, her social media shows her currently at a bar with a bunch of people for new years. Its just upsetting. And I know she's allowed to have a good time but it's not fair. And he's the nicest guy Who just rolls with it. But I'm struggling with never being able to do things with him. That's just me venting. there's no hate. No bitchy attitude. Just how I'm feelin