I didn't read everyones comments but...
It doesn't matter if you are "exclusive" or not. You guys like eachother?! Right?
There's a reason why they still talk (whether it's the friendly relation with her brother or not)... maybe he still loves/likes her?
I understand when former couples have children together, they stay in eachother's speed dial. But your guy seems to be up to no-good.
I say stay away from him, it will just cause more emotional stress and pain for you (currently and down the road).
There's so many guys in the world, date around more. The right one (who doesnt have an ex hanging around) will come your way! Trust me; trust the people with experience.
P.S: From experience, I've learned that "exs" are ex's for a reason and they will never change! So I stay away from my ex's; get rid of all the pics, delete contact #, delete email addresses, stay away from places he hangs around at, stay away from online places he frequents (Myspace?), etc.
I just sum up the experience in my head to make me a better person.
(Example:
Experience: Ex smoked weed A LOT.
Lesson Learned: I will never date weed smokers ever again; they are all the same-- Chinky eye'd losers.)
I guess your "guy" doesn't understand what the word "ex" means.