I totally understand how you feel about H with the OW...it is painful to think that they could even think about being with another yet alone actually being with them...
The best thing you can do is STOP thinking about those things....it won't make anything better....so put up the sign....change your thoughts....when H is there he is THERE with you and DS....enjoy the moment and it will show through....and maybe...just maybe he will take note!
Hang in there....be a good mom and a good person....things will work out....it takes time...lots and lots of time...and I know this is the hardest part...not knowing the end of the matter....but when it is the end, you will know...and you will be fine