Second Class Mom???

So I am having lunch today with two of my longtime girlfriends and they are always looking for the MommaDrama update - which I always have!! I start to explain that we had middle school orientation this week. Timmy is going into 6th grade next year. The first question from them is "Why did you even go - why didn't you just let (hubby) take him?" Now they both have children and they are still with thier babies daddies so I'm trying not to come out of my skin. If Timmy lives with me 1/2 the time and I am responsible for his growing up......why wouldn't I be there???? (I'm pretty sure if BioMom keeps up her crap, we will have him 100% of the time). Anyway - back to orientation.....BM actually shows up. I am amazed! She makes a nice attempt to ignore my exisitance by introducing my hubby as Timmy's father and herself as the mother and just leaves me standing there. I reach out my hand and introduce myself to the school couselor as Timmy's Stepmom. The counselor was fantastic - she involved me in the conversation the entire time. Nice try BM!!
Later in the day one of Timmy's friends parents came up and started talking to BM and my hubby and it was like I was not even there......no eye contact, nothing. I started to think of all of the times similar things have happened to me. Most of the time it is Timmy's sporting events. All of the moms hang out and talk etc. and I am the outsider. I don't know if it is that they see me as the potential outcome that could happen to them if thier marriage broke up or what. I was not even around when my husband split up with the ex but, I get this feeling that I am looked upon as the "other woman". It's particularly challenging since the BM hardly even attends any of his games. Even when she is there when he comes off the field, he comes to me first.....maybe that's what bothers the other moms. I don't know - I just wish it would stop. I am more of a positive influence on his life than she has ever been. I still end up feeling like the Second Class Mom!
One of my friends that I had lunch today stopped by my house a little while after lunch. She felt really bad for what she said and I realize it is confusing for people because half the time I'm saying " this or that is not my responsibility" .....the truth is that I'm confused myself most of the time. Where do you draw the line? I would love to hear your thoughts or opinions. Take Care and Happy Mothers Day to all !