The background is that we became friends when his ex was pregnant. They were very rocky and living in different cities at the time. They had previously been together for 12 years. His son was born in April 2022. Initially he was travelling back and forth and spending the odd night with his ex and son, to give support to his ex in the initial stages of the baby being born and to spend time with his son. However when his son was around 4/5 months old, they began using a contact centre to facilitate contact between my partner and his son, as him and his ex were unable to spend time together due to high levels of conflict between them. I know that it wasn't due to abuse or anything, I saw messages between them. If anything, he claims she has mental health issues and was emotionally abusive towards him, however I have no proof of that.
Anyway, my partner and I got together when his son was around 4 months old. Things progressed quickly and I fell pregnant a few months later. We went on to buy a house and our child has just been born. My partner is still involved with his son, he adores him and sees him every other weekend, collecting him from the contact centre on a Saturday and he stays with us until the Monday, where he is collected at the contact centre by his mum. Him and ex haven't had contact with one another for around a year, son will be 2 in April. Bar the odd text message regarding if son has been unwell etc.
Things are going great, he's a fabulous father to our little one, very engaged and suportive. He truly is a lovely man. However I'm not sure if I'm just being insecure due to hormones but increasingly over the past few weeks, I've been worrying about being his rebound and things not working out between us.
I don't even know what I'm asking tbh. I'm so happy with our relationship. He says he is and I've not seen anything to make me doubt that. But I can't get this feeling out of my head that I'm a rebound and he's going to leave us and go back to the ex. Or regret how fast things moved between us. Am I being unreasonable?