My boyfriend said he is clean, should I trust him?

Yes, But... Yes, but i would still recommend that you suggest that you both go down to your local clinic and both be tested together before you become intimate. Either of you could have an infection and not know it. The experience may provide you with a great deal of information regarding your relationship.
Maybe. As i tell my patients, nobody can protect yourself more than you, so if both of you have been sexually active in the past, then i suggest both parties be tested and always use a barrier/ condom even if you are using other means of birth control.