Boyfriend?

So today I found out that my ex-wife has been dating someone for 3 months.  She started dating him before our divorce was even final....I'm not sure why or if that is relevant but it is true.  The fact is I am not sure how I feel about this.  It is weird.  I had asked her to let me know before she introduced or told the girls she was dating someone.  I didn't want to have to hear it from them or process it in front of them.  So she sent me an email late last night, that I got this morning at work, explaining that she has been dating a guy since April and now he is her boyfriend, and she is planning on introducing our daughters to him some time this summer probably. 
I spent the work day in a very weird place....as I said I am not sure how I feel.  I am a bit jumbled.  Maybe I should be mad, but after everything that has happened, I don't really have any mad left in me toward her dating.  Plus, it's not like we are together; she is free to do whatever she wants with whomever she would like.  Maybe I should be sad and maybe I am....  Maybe I should be shocked, but truth be told I kind of assumed she had been dating.  Maybe not to the extent of boyfriend.  I think that's the word...boyfriend.  Yep that's it. 
I'm not sure what to do with that.  My wife of 12 years, the mother of our daughters, the woman whom I loved...who I still love I think.  The person God joined me together with in a holy union.  This woman whom I share so many memories with, most of them good.  This woman has a boyfriend.  Not some secret, but someone whom she is willing to tell me about and is considering telling our daughters about.  Yes this is the reality I am struggling with. 
My ex-wife and I have remained amicable through this whole divorce journey for the most part.  There have been a few touchy moments about money and the kids, but we have managed to keep our focus on the goal of being the good people we are and staying amicable for the girls.  That is why I believe she felt compelled to tell me, to honor my request and probably also because it is good for the girls.  This reality is probably the thing that makes this so confusing. 
The easy thing would be to hate her, to write her off, to rage and wail.  But I can't.  I mentioned it above I still love her.  That may make me ridiculous or weak or something like that but I don't think that is the case.  What I am is aware of me, my feelings, my emotions.  However, this new reality complicates things for me.  Sure this is painful.  But pain has been my constant companion for the last several...what months, years...I'm not sure.   Pain just travels with me.  So pain would not change anything.  Finding out this news is indeed painful, but nothing I haven't experienced before.  So it is something different, something new...
I'm not sure what it is...it is unsettling.  But perhaps, just perhaps this is the beginning, the beginning of closure.  The beginning of allowing the love that I have to fade into whatever it will be from here on out.  I hope so.