Yes it is weird hes your boyfriend hes free time should be for you not your best friend when it gets to the point where hes texting your friend more then you and your friend keeps texting him and hasent said anything to you about it then shes fine with him texting her alot and they could end up liking each other the more time they share plus some girls you cant trust but it is a problem if hes texting your friend more than you alot it shouldnt be alot for your best friend it should be alot for you and less talking to your best friend
When did they become friends? Before or after you guys started dating? And when did you becomes friends with your best friend? Do you think she likes him? Because if she does, then yes, that could be a problem. It would mean she is being deceitful and is not a very trustworthy friend. I guess it just really depends on how well you know your best friend and your boyfriend. You have to decide whether she is trustworthy and what her intentions are. And of course whether you can trust your boyfriend, which I would hope you can.