I can’t seem to bond with my husbands son

My husband and I have been together for almost 3 years, only married for 6 months. He has an almost 7 year old son. The mother abandoned him as a baby and I’ve kind of stepped in as his mother figure since he was 4. I’m not sure why but I can’t seem to bond with him and feel like he’s my son too. I love him as I would any child I’ve been around for a long period of time but I don’t feel that mother/son connection. I hate that I don’t have that and I really try to feel the motherly love for him. It’s absolutely nothing the child has done. He’s an awesome kid. We had a rocky start because he was totally undisciplined and would act out in a big way for attention but we are past that and he’s a great well mannered kid. What can I do to strengthen our bond, Grow closer and feel that mother/son connection? Please no judgement since I feel so horrible about this already!