I went through this situation as a child and recently with my blended family. Its normal and if you allow your son to voice his feelings in a respectful way, I think it will work out. I would also look for him trying to manipulate you and his bio-dad into getting his way.

For me the most important thing was being listened to and having a voice in the family. My step son and I get along great, but it was rough in the beginning because he didnt want to share his mom. I think someone mentioned a date night, I think thats a great idea. Good luck.