He needs to only have communication with her that relates to his children. No more no less. When that happens her crap will stop.

I can totally relate with your situation, the bm in my life pulls the same crap with my dh always asking for favors from dh when stepson is with her. Finally after years & years of this I told dh or I asked him to "make her parent" because alot of her favors are just basic child rearing skills. This bm has not a maternal instinct in her body. I asked him to stop answering the phone and let her leave a message, and stop these favors. I am lucky because dh did exactly as I asked and that part of our lives has gotten 10X better in the last few months. Except now stepson acts different towards me, not sure if he's being swayed to disobey by an angry bm or because he's almost 13 but it seems like his attitude with me started about the same time as dh stopped being so available to the ex wife.
So in a way I just have a different set of problems, one step forwards two steps back I guess.
Oh and the other problem is text messaging, now
I know I use text messaging alot and it is rather convienent at times but you can't control a text messages text, you can ignore calls but texts give you information that sometimes you don't want to know. The bm in my life likes to text my dh about stupid stuff, sometimes having nothing to do with their son "did you know so & so & so & so are seperated" And One of her big obsession is death, she likes to be the 1st to tell him and she'll do it by text, "so & so died" or "your 2nd grade teacher died" or "so sorry to hear about your uncle". She's in insurance and a big gossip hound.and it's hard for my dh to not respond back because you know it's death but I have convinced him that people die all the time and you usually see it in the paper but for some wacko reason she thinks she had to be the 1st to tell people. He very rarely responds anymore thank God.
Well hang in there, talk with dh set up boundries and follow thru so far things have been going decent but they never stay that way very long.
Talk later, Crystal (biological stepmom)

Ignore. Don't even reply. Just, ignore.

Although, it can sometimes be fun in that totally bad for your mental health kind of way, like when BM asks DH for something, we spin it so as to accuse her of being an inadequate mother, or having an inadequate husband (her new husband who she has a baby with).

Like, she has asked us to watch the kids (my skids) because she has to take her baby somewhere. We respond, 'If you are unable to care for the kids during their time with you, I would be happy to change the custody schedule to take them.' Her response, 'No. It's fine. It's just that my husband actually works.' Oh, so, I guess mine doesn't. Why the hell is he gone so much then, huh? See. It's not good for my mental health, but just knowing how much that pissed her off, to insinuate that we should take the kids, ha! I love it. So petty, but I do. I feel like it's my right to do that to make up for all the crap I have to deal with. Messed up way of thinking, but funny.

The other trick is to show compassion, but still say no. Like, when she said that she and her husband were having money issues and its causing problems in their relationship so she needs us to pay for some stuff she bought. We say, 'I'm sorry that you and your husband are having financial and relationship problems, but I never agreed to paying for the things you bought.' We didn't even get a response to that one. It makes me wonder if her husband knows she is going to DH telling him they have problems and asking for his help. Wouldn't you be furious if you were him? She would do the same thing to DH when they were together. Calling his parents saying that he isn't providing for her. You know what the reasoning behind that was? Because he didn't buy her a designer purse for her birthday. Who does that? That is like the lowest of low. But the worst is that he gave in to that kind of manipulative bullshit and her new husband probably does it too. Sounds like your BF is doing it as well, so it's gotta stop, cold turkey.

I have to agree I would not respond at all. My dh doesn't either. Like the thing about the cars, she texted saying that "I guess you will be buying the boys a car too" (I bought my kids a car while knowing that bm's aunt is buying the boys a car when their time comes). Dh didn't respond, but then 2 days later he had to talk to her about our vacation and what she was going to do about the 4th since she has them for that day and we wanted to leave 2 days before that. She agreed to let us them. But NEVER said a word about the cars???

Anyway my point is if you don't respond that crap she may get the hint your dh is not going do anything for them. But do respond the ones that are necessary for the kids. However I want you to know that it may not stop like with my bm she still texts dh for stupid crap and thinks he will help her. The best was when she got a computer and wanted dh to install it. He ask can purpledaisies come b/c we have some other things to do in town? She said no ummm wonder what that was about? She tried a few more times to get him to come over for the computer saying 'but the boys need it and I can't get it going, it's for them.' umm sorry call a professional!

My point to that is it may not ever stop b/c bm may never get the hint.