<human>: Just as a bit of background, my SO and I have been together for 4 years and he has a 9 year old son to his ex girlfriend of 10 years. The start of our relationship was rough mostly due to my unmedicated BPD and his unmedicated bipolar but we're in an excellent place now and have been for awhile. Yay meds! 

Yesterday my phone rang and it was my SO's ex. My SO had asked me to text her to let her know the arrangements for picking his son up as he had no credit. She called thinking it was his number so I politely answered and told her this wasn't actually his number. I then texted her 'sorry about the confusion, 'SO' gets me to text you as he never has texting credit, here's his number'. Not long after my SO contacts me via what's app and tells me that she called him and broke down. This is how the conversation went and I have been feeling weird about it ever since.

Her: I just wanted to tell you that you were a great partner.  I'm sorry I didn't see that.

SO: thanks

Her: I feel like I made a huge mistake, we were such good friends. I wish I tried harder to make it work.

SO: You're happy now though...

Her: No I'm not.  are you?

SO: Yes.  We have been through a lot of rough times, but I can genuinely say I'm happy. Why aren't you happy?

Her:   He doesn't listen to me, he doesn't understand me.

She was crying by this point and said she had to go and hung up the phone.

The man she is currently with is the man she cheated on my SO with and left him for.

I know my SO has done nothing wrong here and I've explained that to him and that I'm not mad at him, I just don't know how I feel about the whole situation. My SO said he just feels sorry for her and feels obligated to tell her to see a shrink.

How should I be feeling Reddit?

Can you condense the text into a few key points?
<bot>: SO's ex told him that he was a great partner and that her current boyfriend doesn't understand her. Not sure how to feel