Rubbish. Utter twoddle.
There's no need to break up with him - everyone has their unique set of morals. No one on here can tell you how you feel about him. Certainly, in some situations pulling other people can be an indicator that you're not entirely content with your boyfriend, but at the end of the day, I don't know about you, but I love lots of different things about lots of different people, and my boyfriend, as amazing as he is, isn't 'lots of different people', so there will always be that attraction to other people simply for exerting traits which I find attractive that my boyfriend may not possess.
This doesn't mean I love him any less.
I suspect you're not feeling guilty because you feel fairly certain your bf won't find out. I know in your situation I would feel worse about hurting him than committing the act.
Don't dwell too much on it and don't bring this up with him in an argument just to hurt him. If you eventually feel like you 'have to tell him' then that's up to you but from one morally dubious person to another, (by TSR's standards, anyway) just forget about it and focus on your boy for the meanwhile.