Am I overthinking to not go on this trip?

My ex boyfriend invited me on an overnight trip, and I declined because I didn’t feel it was appropriate since he now has a girlfriend. He says he no longer has feelings for me or is attracted to me and is so in love with his new girlfriend he feels she’s the one, but I just felt it was inappropriate.. even though we were to be sleeping in different rooms. When I declined he made me feel I was overthinking it and it’s not an issue. She lives in a different state and I don't know if she even knew he invited me to go.. it just didn’t feel right.

Am I overthinking to not go on this trip?
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