So I'm sexually attracted to my boyfriend's brother...

I've been with my boyfriend for 4 years and I love him with all of my heart. I'm pretty certain that he is going to be the man I marry. However there's one issue..... Recently I've been having feelings for his brother. His brother is my age, whereas my boyfriend is 3 years older than me. His brother comes over to hang out with us literally every night, and I enjoy him coming over cause he's a lot of fun. However, in the last week or so I've been feeling a sort of sexual attraction to him. Obviously I am NOT going to act on them at all because I am in love with my boyfriend. I think these feelings may be due to my boyfriend's very low sex drive. I typically initiate sex and he's told me that he just isn't as interested in sex in general. As a result im starting to have these feelings for his brother since he's always around.. How can I get rid of these feelings?! I never want my boyfriend to know I feel this way and I'm not gonna make him stop having his brother come over. Any advice helps but no rude comments please, I'm stressed enough as it is....