I need some tips.

I'm a newly single mother. I still see and talk to my child's father. We don't see each other as often,but we do see each other. I'm having a very hard time with dealing with our split. He makes it no better and I'm guilty as well since we broke up we've had sex 3/4 times and with him I can never make it just sex I always get my feelings in and then I get angry. I want to be mature and keep things nice and cordrial for the sake of our child. I know my first step would be to STOP having sex with him. This morning he asked me to pick him up from the dealership because his car was being serviced. The bitter part of me wanted to say no, but I didn't want to seem like a bitch so I did. When I arrived he's outside on a phone call smiling and laughing then walks inside the building when he returns conversation is over. I got sad then mad because I know that he's seeing someone. I wish I would've just said no and let her pick you up. It's so hard to be mean to someone you love and invested so much time into. I want to keep everything business just strictly about the child with him. No I can't do you favors, no you can't just spark up conversation with me at your convenience and certainly NO MORE SEX. Any other suggestions?