your stbx isnt going to go to counseling with you.
she's done and moved on.

and you guys dont need "joint' counseling to be better coparents.
good coparenting is a choice.
you both are mentally able to Choose or not choose how to parent together and apart.

it will make no difference for you stbx to hear how you 'feel' about her boyfriend being around your daughter.
all it WILL do is cement them closer together as they will be 'fighting' against you. AND it will be good 'stuff' to use to mock you when they are together.
YEEEAAHHHH!!! no conseling together.

additionally...often when people are suggesting this kind of thing it's an unlying hope of contact. when you look back you will see this is most likely the case for you too.

forget about your stbx.
do what youre doing.
and
keep moving forward.

right now youre dating like a fiend to forget your stbx,
to prove to yourself and to her that y ou are still a great, attractive guy that women DO want to be around.

eventually you'll believe that! 'cuz you ARE!
then youre dating will slow down.
you'll be used to you stbx's boyfriend,
and
you'll feel even better than you do now.