<human>: Can you condense the text into three sentences or less?

Me and my ex dated for 3 years, and broke up a year ago. We lived together, and it was serious, but we broke up because we have fundamental incompatibility issues. The breakup was amicable and we are still friendly, occasionally messaging. I started dating someone a few months ago and we are much more compatible. My ex knows my new boyfriend through friends of friends. They have met once, accidentally, and it was all fine and friendly. 

My ex has a new girlfriend, and I'm genuinely happy for him. My boyfriend and I are going to an event hosted by my friends, and I know my ex will be there as he is friends with some of them. It will be small enough that we will definitely bump into each other. I'm fairly sure his girlfriend will be there too; she is not part of this friendship group at all. What I'm wondering is how to behave to her. I have no idea if she knows I'm the long term ex, and no idea how she feels. I don't know whether to just say hi and then disappear, or try to be friendly, introduce my boyfriend and show I'm not a threat... Basically I want to make this girl feel comfortable and welcome. She's coming to a party with loads of my friends and from being with my boyfriend and his friends (who are friends with his ex) I know how hard it is. What would you recommend I can do (if anything) to help her feel more at ease?
<bot>: Ex's new girlfriend is probably coming to a party hosted by my friends, what can I do to make her feel welcome?