my boyfriend was honest to me.

He told me he had a feeling or lust for this girl while they were away for a week with church members. He said nothing happened because everytime, there seems to be stopping it. I asked him what if nothing stopped it? Well, i guess they'll DO it. Should i trust him? He said, he made a mistake to be weak by that time and that he loves me.because a feeling with lust is not love, and that's what he had with that girl. Should i trust him?