Need relationship advice

I just recently started dating this guy in college. He has a lot of friends that are girls , and I have trust issues. I walked into a dorm party with him sitting next to a girl on a bed and kinda freaked out because I assume the worst. And then he told me she’s had the same boyfriend for two years and to not be mad because nothing happened. I’ve been cheated on before and I get really paranoid especially when alcohol is involved . I’m going home for the weekend and I’m scared but I have to learn to trust him :/ how do I get over this ?