hugs to you.
I get the same sometimes...like DS (8) will go on about "can't wait to see ex" etc and on a bad day, it really hurts. It is silly, but i feel rejected!
Could you say "I am so glad you love your dad, he loves you too. However, mummy would love to focus on what we are doing here for a while"
DS is a very mature 8, so the other day i spoke to him about how I felt and he understood and stopped going on and on...but, at 6, i don't think I would have. At 8, he is able to understand he can talk about anything he does with ex etc...but that the "i can't wait to go to his house" over and over, can be a bit grating.
Keep up with the distractions...and be really kind to yourself.
Does he know when he sees him? I only tell DS the day of the visit now (due to lots of past disappointments) and this seems to help too.