Should I let my best friend know about the nature of his new girlfriend? Should I tell him or leave it to karma (Fake names are used!)

In short, Jake and his girlfriend (Helen) already knew each other ages ago since they had a “I don’t know what we are” type of thing.

After they stopped it, he started to and still does really like another girl (Maria) but they can’t date because of situations.

Some time ago, I met Helen not knowing that her and Jake had history.

A few days ago, Jake and I went to Sam’s house and his girlfriend and Helen were there.

Within a few hours Helen and Jake were acting coupley but i didn’t find it too weird because Jake is often flirty and he has a lot of female friends so I didn’t really think much

After, Jake told me about Helen and Maria and that he wants to date Helen but still likes Maria. I gave him advice and he made Helen his girlfriend and let go of Maria

Recently I went to Sam’s house to see his mom since we’re close. She said she doesn’t trust Helen around guys because she’s too flirty and always seeking any male attention. I’ve noticed too

She said that ever since she started being around guys all the time, she’s been dressing too revealing but was dressing normal before. She’s been dressing like this around Sam and hugging him like his girlfriend would

3 days ago, LITERALLY 2 DAYS after Jake and Helen became a thing, a bunch of older guys (19–24) were at Sam’s house and one of them tagged along with us (Sam, his mom, Helena and I). All day, Helen (basically in a bra) never spoke to him, was just looking at him every so often and he was just minding his own business. During the ride home, suddenly she wanted to go back to Sam’s house to obviously see the boys even when his mom said she’d drive her home. The guy and Helen were next to each other in the car and she was practically sitting on him every time the car turned. And I barely moved smh

Jake really likes her and I don’t want him to get hurt or feel like I contributed when it could’ve been avoided. I feel bad because I kinda helped him decide to date her and now she’s doing this