And should I be worried?

A couple of months ago, DS4 missed a couple weeks of preschool because of days off/illness. (He only has preschool 2 days/week.) He did not want to return after having so much time off, and he had episodes at the door of the preschool. He would only let go of me if he said "i love you mom" and kissed me about 20 times. I let him do this twice, then I told him he had to get all his i love you's out before we got the the door of his preschool room. Since then, he says "i love you mommy" on each step on the stairway down to his preschool room, and with each step he takes until we get there. At first, I told him that I loved him too, and he didn't have to say it so many times because I knew he loved me even if he didn't say it at all, but he still does it every day of preschool. I just ignore him. Other parents have seen this and said "how cute" and so I try not to look so irritated while I'm ignoring DS4. (Cute once, irritating when it's all the time.)

Should I be worried that this is an OCD behavior? Is there anything I should be doing besides ignoring him? Thanks!