No expert on the social dynamics of girls as I am a 19 year old guy but I'll try to explain what I think is happening <3

Like I said, my social circle is much smaller than hers, so she was kind of my "in" into the group we went with last week

Well, she is the one doing the inviting, so it's the size of her circle that matters :/

Everything was peachy keen until this morning when I was making the usual rounds on social media, and see a picture of Ashley and the group of girls at the game

She clearly just didn't want to tell you she was going and tell you that you weren't invited, she did it to try and be nice not nasty.

but I just wanted to talk about my dumb problems with somebody.

Yo, I had this happen to me every week for 7 years in between the ages of 11 and 18, it isn't a dumb problem <3.

You are good friends with Ashley, maybe ask her why she lied to you (probably to not upset you) and tell her that you would really appreciate being invited to these things.

I had a good friend who I asked to do the same thing, he couldn't do it because his friends would have disowned him for inviting me, but I still thanked him for trying to get me invited.

Also, remember that facebook only shows the highlights of people's lives, it's not a balanced representation. Not everyone is going to a party every week, even though it looks like it.

I went through something similar and I am a little bit older and I have solved the problem for myself, so if you do want to talk then feel free to message me or reply to me (it's my throwaway but I check it every couple of hours unless I am sleeping)