Not seeing partner as often sucks...

So my partner and I have been seeing each other every 3 weeks, that’s the only time we have sex. Which it’s kinda bothering me. He shares custody of his kids with his ex wife. I know his kids come first. I asked him when are we seeing each other again and his Answer was, I HAVE TO CHECK MY CALENDAR 🤔. Which made me think. It’s been 4 weeks today and we haven’t gotten together. My question to you ladies is. Is this guy still interested in me? Or Not??? How do you not know when you will have your kids again and know when you will have time for me. I don’t get it. Please help me out. Thanks...