Is she lying, should I stay?

So (male) Ken and Lucy (female) been dating for a, about 4 months. Ken came over as usual to spend the night at Lucy and found a condom in the bin Lucy said she used it for her dildo and girls usually do this. Ken didn’t know what to believe but got over it. Later that week Ken saw a guy come over to Lucy’s house and after the guy left Ken came in asked Lucy if there’s anything that’s happened today and she’s not said Lucy said she promises nothings happened. Ken gave Lucy time to come clean she didn’t until Ken left saying I saw a guy and came into your house for over an hour, Lucy started crying saying she felt stupid because she wasn’t honest because Ken may think something happened but nothing happened. Ken said he can’t do this anymore and tried to end things Lucy said she was honest and wants this and still loves Ken. Ken said he need time to get over this because it’s too much. Later that week Lucy went out with her girlfriend promising Ken she loved him and nothing would happen. Ken in denial and slowing becoming toxic had a stake out on Lucy and saw her kissing a guy in the club and came back home with 2 guys and her girlfriend. Lucy next day never told Ken until Ken asked over and over till the point he had to say he knew. Lucy cried and said nothing happened. Ken is confused now please help
Is she lying, should I stay?
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