I just need to know if this is normal? Does this always happen?

I have a son who is a year old. Me and his dad broke up right after he was born, so it’s been a year since we’ve been broken up. I dated this one guy for like a couple months back in March and it didn’t work out, figured he was just a rebound and I had feelings for my ex still. Then I met my current boyfriend in July and we’ve been together since then. I feel like I love my boyfriend and care about him so much, but yesterday, I went somewhere with my sons dad for him to play. I brought my sister with me because being alone with him in the past always just made me feel upset since we weren’t actually a family anymore. All day yesterday, I felt fine. We got along. In fact I remember leaving and thinking I’m so happy that I am finally over him and we can get along and be friends. A few hours after getting home, I just felt this overwhelming sadness all of a sudden. I just felt like I missed him. As the night continued last night. I stayed over at my boyfriends and we watched movies, cuddled, basic stuff. Cuddled this morning too. Got up for work and as I’m driving, boom, the feeling comes back to haunt me, I feel this sadness, then it goes away. What does this mean?? Like is it normal to always feel this way about your child’s father? Does this mean I don’t really love my boyfriend? I need help 😐