child abondonment issue i think? not sure how to deal with it or if i should just back out...

So a little background is this...I am a mom of one 7 year old little girl, i have been with my boyfriend for about a year now and he has a little boy.  He was divorced a few years back, and the mother of his son is horrible.  She goes out every weekend, doesn't check on him, doesn't call.  I am concerned with the situation.  He cries at night, he will only stay at a close relatives houses, he never wants to be with his mom, he has even told teachers that his "dad will be there his mom is to busy partying."  So i mentioned to him today, because he always says that his son wont stay with me, (which i think is important because he needs to be comfortable with my daughter and i since we are planning to move in together...and i am now 16 weeks pregnant.)  I feel like he needs to be able to feel comfortable in our family and that he is welcome to be at our home at any time.  His son has no idea that i am pregnant yet because he is scared about his reaction.  Which i understand that he has gone through alot with his mother leaving him at night and not being at emergency room visits and many other issues, but i feel like there is a better way to handle it? I am not sure what to do because all that my boyfriend said is "I know."  Should i just let my boyfriend handle things with his son, is it to much for me to jump in and say that he is babying the issue to much and that he needs to be more open with him, so it wont cause more issues? Where does a "step parent" because that is what we have been talking about, draw the line when there is a combined child in place( with us having a child together and raising our child but also children from separate relationships)?  

[raquelplus2]

first off iam sorry that your going through this and that poor lil boy as well. i think in my opinion that you should def be honest with your bf and tell him how you feel bout that situation and def let him no that you care for his son and how you feel bout the situation in a very understanding n loveing way. you said realy nice on here and what i got from what you rote is that you care alot and want him to be and feel part of your guys growing family and thats a very good thing considering that most step moms dont accept other kids like that uno. but i ould talk to him and be involved after all you guys are family now and you do have that right as a stepmom to state your opinion  but ultimately it is up to him but you have say as well. goodluck i hope all works out for you n your new family!