Guy and Girl advice, please.?

So, I've liked this guy for 2 years now. I started liking him the first day of 6th grade (he's 2 years older than me). He didn't like me back then. But the following summer (before 7th grade) i stayed the night at his house and we ended up making out. (Me and his sister are best friends) Now its been 2 years and the past couple weeks we've been hanging out alott. I stayed at his house for a week and he stayed at mine for a week. It's been reaaly fun, and we're going out. But no one knows that. Hah. Anyways, I just need to know what everyone else thinks on the matter, his sister gets kinda sad that I'm ditching her for him.. waht do you think i should do?Guy and Girl advice, please.?
You can still have fun with your boyfriend, but also try to get some time with his sister, or possibly do something all together.

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