I understand that communication problems can ruin a relationship, but you just need to be open and honest with him. If you really need to be sexually active, either tell him this or stop seeing him, because if you keep cheating on him, you're both going to get hurt. I think you need to be completely honest with him even if it means a break up because a relationship built on lies isn't a very good relationship. Hopefully if you stop seeing the other guy and remain completely faithful to this guy, he will forgive you and you guys can try to work at your relationship.
But maybe the other guy is who you really want to be with because he seems to share the same interests and priorities that you do. If the sexual aspect is that important to you, it's probably not a great idea to be with a guy who isn't ready for that yet. I hope you guys can talk it out.
Tanya in Austria