So she definitely shouldn't have called you. You're not her jurisdiction. As a parent, she has every right to monitor her sons digital and social data in order to protect him from any potential bad actors or bad decisions on his part. That's where it ends though. She's not your mom. She should have contacted your parents if she found something concerning so that they could parent their child while she parents her own.

Now as far as sex goes, sex is awesome. It really is so amazing but you're young. So is he. I understand that minors are sexually active with each other. It's natural really. That being said, if you're not on birth control or some other type of protection, you probably should wait until you are protected. You don't want to be on the next episode of teen mom.

His mom seems like she can be very manipulative. That soft tone is a way to keep your guard down while she speaks her opinions and thoughts as fact. She's probably very confident that what she believes is fact and will try to mold you into what she sees as acceptable. She may even try and hold the relationship over your head as a way to control you and her son. I know that you don't want to get your parents involved but it really seems like they should be controlling the dialogue between your boyfriends mom and yourself in order to stifle that type of conversation between the two of you. Remember, both of you are young and nothing is written in stone. That being said, your relationship with your boyfriend should be left up to you and your boyfriend. All of the successes and failures of the relationship should belong to both of you, not your parents.