Cheating?

So I've been with my boyfriend for nearly two months, I got to know him very well before hand. I feel extremely guilty with myself because I keep fantasising about sleeping with other guys, but I've never actually done it. I took his virginity, because he wanted to lose it. He's a good boyfriend but he's terrible at sex. I'm not in the relationship at all just for sex but it's a bit off putting when he can't get you to orgasm. Help?