I still love my soon to be ex-wife but we have been going thru a div...?

We have been going tru a divorce for quite some time now(nothing reconcilable she has decide to start her love life with someone new which is perfectly since it wouldn't worked between us anyway..but how do i go about telling my now 3 year old son to not tell me things that she does with her new boyfriend since it still bothers me knowing. I don't want to tell my son to not tell me i still listen to him because i don't want to say don't tell me certain things and if one day there is really something he needs to tell me and wont because of me saying i don't want to hear about them two. How do i explain to him considering he is very young to not come and tell me everything he has done with his soon to be new dad? Hope this mess makes sense...sorry!