Stuck in the middle

Okay, so I me this guy and have been seeing him on and off for a year and 1/2. He did mention he was single when I first met him. He is much older than me. He moved too quickly and I told him I wasn’t ready for a relationship. We would meet at his house most get togethers. But recently he would ask to come to my place, or if we can meet up else where. Suspish. So, I did some investigating and found out he recently started dating again. They’re official on social media. My point is, should I let the other girl know he’s been messaging me to see him? I just want a smooth exit, no drama, but I feel bad for her. I would want someone to warn me of him, if I was in her position. But then again, I don’t want to ruin anything between them.

FYI, I have been blowing him off for the past few months and he keeps trying to see me.

I would tell her. Just a causal message saying that he’s been messaging you, send the screenshots, and say you just found out after seeing his social media. I think she deserves to know, any girl would. I know some girls get upset about it or whatever but at least you know you tried to help.