Separation anxiety?

In the last month 1/2-2 months my SO has been working long ours. Our son picked up on it pretty quick. He realized if he woke up an hour or so after I put him to bed he would get to see daddy. At first I felt bad and would let him stay up and spend some time with his dad then try to put him back to sleep. It got hard putting him back to sleep and I was drained (since I haven't even been to sleep yet) so I started putting him in bed with me so I could get some sleep. He also grew more attached to me since he didn't see his dad much anymore. Now it's like he will only sleep with me. He does OK for naps usually but bed time is getting a lot worse. How do I get him back to sleeping in his bed and staying asleep?! Please help!!!