In relations like this it is impossible to get a clear closure with conversation.you will get closure with time, with acceptance that it was a past and has ended with whatever note. What is important is your present if you and your partner are open about each others past and are amicable you can meet your ex but in most cases (not alway) there are chances of being inclined towards your ex maybe temporarily but  then that can be an issue. Rest you are mature decide what is good for you and for people around you.

I have just read through your scenario. Closure is very important for any kind of relationship. Setting boundaries in any relationship is very important. In any relationship it is important to set boundaries on what to share and what not to share and it's also about personal boundaries. With respect to your situation it extremely important to have a closure and it is your take on setting boundaries and how you feel about setting boundaries. If you want more help you can contact me Hope you found this helpful.

As long as your conscience is clear, and your present boy friend believe you, you can definitely go ahead