Why is my girlfriend that way ? ?

I am real mad at my girlfriend cause I fought her looking at this guy that works at the local drug store and this is not he first time I catch her doing this. She looks at him like if j was not there and not onl at him sometimes guys look at her and she looks back and stuff u know and she acts different I confronted her we got mad and I called he really bad stuff like she's a ska*�! And w not. I forgot to mention that she's almost due with my girl This month. So what do you guys think? Wt do I do? Why is she like that. She's 3and a Hal years older than me .