Advice please!!!!!

So I got on my fiancé phone just now and there was a girl from his school he's been giving a ride home and I read their texts just now she sent a middle finger and he sent a ? And the she sent laughing faces and then he said you would and she responded with you dont know that and he sent a ? I'm like freaking out right now and don't know if I should be worried he's cheating or not 😞 I'm tired of being hurt and let down I just keep feeling like a waste of space and I'm wasting my time ...