Slept with ex, found out he dating someone new, should I tell her

The background on this is I dated a guy for about a year. I ended it because I basically didn’t trust him. Thought he was probably cheating (always keeping his phone upside down etc.) tried to address those things with him to no success.

The further background is that when we first started “seeing” each other a year and a half ago, he was in a long distance relationship but was unhappy (apparently she was difficult) but he apparently had too much anxiety to end it. I was super hurt by this situation and I eventually told him to leave me alone. Two months later he contacts me single. So I agreed to a relationship despite all that (idiot).

Anyways… I ended the relationship in January. He has still be texting me regularly as friends. Like daily back and forth. We got together for drinks about a month ago, I was thinking maybe of giving him another chance (idiot). He didn’t mention he was dating anyone and I didn’t ask, but he would have lied anyways. I slept with him (idiot). Then I ask him what he wants. He says to be friends for now.

Anyways I instagram stalked him a few weeks ago and saw a woman has been posting pictures of them together since January. So I asked him if he is dating anyone, he says no. Now I can see her posting pics of them together on an oversees trip. I have now blocked him (a girl eventually learns the lesson).

I feel bad for this new woman. Maybe she doesn’t know what he’s like. My policy is never to interfere (obviously I never messaged his ex while we were “hanging out”) but I’m tired of these dumbass men and feel bad.

Should I message her?