Missed out on my own babies birthday.

So my sons birthday was on Monday he turned three! Holy doesn't the time fly !!
I missed out on it. I'm the woman who gave birth to him, raised him on my own for 2 and a half years. Until his father decided to knucle down. To the beast of his abilities anyway. To me any effort from his father is better than nothing, at least he's trying. To me my ex is a horrible human being, but he really is trying his best to be the BEST dad he can be. Which hey, good enough for me.
My son usually spends Friday afternoons through to Monday afternoons down at his grandparents with his dad, every weekend, not every second EVERY WEEKEND. And it's great. I've finally got that little bit of time to myself that I've never had before, mind you I spend the whole weekend off working but that's my choice. I think it's pretty great his father is while a little unwilling to do it he still does it.
He just has a bad habit of using it against. This weekend for example, he was meant to bring my son home Monday so I to got to spend his birthday with him. But he hasn't and he has said he won't bring him back until he knows I won't take him anywhere.
All because I said I was taking him to Cairns for a holiday over Easter. I think that's within my right, it's only for 5 days. And it's to see family my son never even laid eyes on before.
He does this to me all the time. He knows that I work Friday Saturday Sunday. And often he'll drop him off Thursday knowing he will give me less than 24 hours with him because I have to work. I can't not work, I need the money. He can be so spiteful sometimes !
I don't have a question, I just need to vent. In soooo frustrated. I have no clue what to do about it anymore. It's like a vicious cycle that's never ending.
We get along great for a few days and then this. I feel so guilty that there was nothing I could do to be there in my boys birthday.
I guess I'm just glad he did have a good time with his dad.