Most Helpful Guy
It sounds like maybe you don't think you're desirable as a girlfriend so you're suspicious about why a guy would show interest in you.
Certainly it's good to be wary since there are a lot of guys that only care about women for sex and not for a real relationship, but as long as you take it slow and wait on sex until you're sure he really cares about you as a person, I don't think there's any need to be more nervous just because he expresses interest first. If you think he seems worth getting to know better, go for it. Personally I always like it when a woman shows interest in me because then I know I won't get rejected if I approach her.