Orgasm/vibrator/boyfriend

Okay so I've had sex with my boyfriend multiple times but I've never orgasmed and I've always been curious so I bought a vibrator and played with it and I've been able to orgasm with it. How do I tell my boyfriend that I bought a vibrator and did this? We've talked about them before but I didn't tell him I bought one. I just don't want him to be upset when I tell him. Especially since I'm not one to masturbate all the time; more like once a month.