<human>: Can you succinctly summarize the text in 1-3 sentences?

Myex-girlfriend, call her Alex, and I used to be great friends before and after we broke up. We used to see each other often and once in a while fool around. 

When she got into her relationship with her boyfriend [20 M], she stopped contacting me. She told me that her boyfriend didn't want her talking to me and I respected that since I didn't want to cause any dramas in her new relationship.

Recently, she broke up with her boyfriend and now wants to be friends with me. The issue is that my girlfriend [22 F], call her Kat, loathes Alex as she was my ex. I haven't told Kat that I've been talking to Alex again.

I've been talking to Alex for 2 weeks now and have gone out to lunch with her once. Everything seemed normal and I enjoyed it. Last week, I spoke to Alex about the boundaries of being friends. I told her that there can't be any physical interactions and that our relationship is nothing more than friendship. I wanted everything to be clear so that it wouldn't jeopardise my relationship with Kat.

Should I tell Kat that I'm talking to my ex and that I've set boundaries or keep it a secret? If I tell Kat, there's a possibility that she would want me to cut Alex out of my life again.
<bot>: Best friend/Ex-girlfriend broke up with her ex and has started talking to me again. Current girlfriend hates my ex.