Me and my boyfriend been together on and off for three years. Before we met he had these two beautiful girls, but he never got to see them. Now all of sudden he is getting full rights and they are coming to live with him. All this hit me in one day. I know I can be a good mom to them and this is a good thing I guess because I can't have kids myself. But I don't know what to do at all? Please help me!

First, not sure of all of the facts, but they have a mom, you will be at this point the boyfriends girlfriend, not even a step mom at this point.

He may have to have contact on a regular basis with his ex and the kids may be talking off and on about their mom.

You have two choices, leave and don't get involved with the kids. Or be there and help him with the kids.

What worries me is the "off and on" the kids need a steady environment, not a off and on person in their lifes.

I agree that an 'off and on' relationship with your boyfriend isn't going to do children any good. So you either have to learn how to communicate, compromise, and be tolerant of each other or not have kids.
Second, chances are the girls might absolutely be miserable with their dad and with you (a total stranger), and want their mother. They may say they hate you from day one, or cry, or act up just to be able to go home, or all 3. Are you ready for this, despite your feeling that you would be a good mother? It's going to be tougher than getting along with your boyfriend, and you haven't been able to get along with him yet.

Yes, the normal comment, that may not even come out for a while, "you are not my mom, you dont have any right to tell me anything"

Now many step parent relationships work great, but almost all are going to have days that are more like WWF Cage Match.

Even if they are your kids, I have my son and also my niece living with my wife and I now, I told my wife tonight, we were not parents today, we were referees

True, but the I don't plan on walking out on kids... I love kids!!

How old are the kids?

Why are they coming to live with their dad when he had so little contact before?

These are all things you have to take into consideration.

Younger kids are usually more willing to accept someone else in their parents lives. Teens and preteens can be more difficult.

If the mom is sick, dying, or has emotional problems, then these kids will have a lot to deal with, including living with their father, someone they haven't spent a lot of time with (according to you), and a person that will take on the role of mother, but isn't their mother.

This is not going to be easy.

I would really consider therapy for all of you. Not only to help you adjust to them, but to help them adjust to all the changes they're going to be going through because of this new custody arrangement.

Something extreme must have happened if your boyfriend has full custody of the children now, first and foremost the children's health, both mentally and emotionally must come first, they above everyone else involved have no choice in what happens.

Your boyfriend has to learn how to be a father, a daddy, a parent, that in its self is difficult from day one, never mind a few years down the line, yes he's going to need support, and that's where you come in, you stay in the background and let the new relationship between father and children develop, they do not need a mother they have/had one, they are not a vehicle to meet your need to mother, to bond with you only for your relationship with their father to end.

This is going to be a very difficult time in their ( the childrens) life, you have no responsibility towards them, they are not your children to walk away from, so you can walk away from this.

My advice is take a back seat now, support where you can, don't offer advice unless your asked, and protect your own heart, its easy to fall in love with children, especially hurt children, if your relationship ends, if your boyfriend decides he needs to concentrate on his new role and lets you go, your going to have a double whammy of a broken heart.