Can my boyfriend have a std but i dont?

Yes, possibly: It is possible for one partner to have an std but the other not to. Some stds are not 100% transmissible. Hpv, herpes simplex virus, are examples. It can be hard to tell whether or not someone has an std, they may not have any signs or symptoms (and, may not be honest about their status). It is always wise to use a condom, although they do not always protect effectively against all stds.