My gf told me her cousin tried to her but when she sees him she talks to him like nothing happend?

Well my gf told me her cousin tried to her but when she sees him she talks to him like nothing happend at all! She says she was in the back seat of the car and he went back there whit her and tried kissing her and she said no but that he got on top of her and hold her down and tried pulling her jeans down but he couldn't do it so he pulled ou his and Tried tp pull her jeans down again but befor he did anything else he d and got of her and acted like nothing happened she didn't tell until a month later after it happened she said she was scared to tell cuz we had found out she was pregnant and she tought I might have denied the baby we had unprotected for 3 months and she never got pregnant so obiesly u know my biggest fear there even though he never d her could she get pregnant? I wanted to believe her story but a week before she told me we saw him at the time I had no idea wat happened and she was talking to him smiling like everything was fine if some one tried to me I don't think I would wanna talk to him I don't know if she did have whit him and told me he tried to her so I won't think she cheated on me and denie the baby being mine can some one pleas help did she really get d? Or no our daughter is a week old and I love her to death and nothing would change that but I just have to know the truth how could I tell if she did or didn't