Hi there queenoftask, and welcome to Scarleteen. You've asked a few different questions here (which I'm glad you felt comfortable asking us), about masturbation, how you might know when you are ready for partnered sex, and also decision making when it comes to approaching a partner.
To start with the first, there isn't such a thing as a "healthy masturbation schedule". You can follow the schedule that feels right for you. If you feel that you can choose when, where and how you want to do it, and you feel like it doesn't interrupt or intrude upon other parts of your life (like seeing friends, eating and keeping up your hygiene), and therefore all is feeling good, then you don't need to worry. You can read more about this and masturbation in general in our articles: Going Solo: The Basics of Masturbation
In terms of sexual readiness, sex is definetly something you should think about before doing it, not just the first time, but any time. We have a great articles about this on our main site. As a start, have a go at reading this one: Ready or Not? The Scarleteen Sex Readiness Checklist
and come back to this conversations with any thoughts, questions, or curiosities you may have about it, if you feel comfortable sharing those.
With regards to the people you are talking about, whilst it is okay to have fantasies about a crush, revealing your feelings in a way that would disrupt/infer that they should end they are currently in is not respectful of that relationship. That can be super hard when you're feeling strong feelings for someone, however if you imagine if someone did that whilst you were with a partner you can imagine how that might feel. Does that make sense? Also, are you comfortable expanding on whether your friend told you this before or after she started this relationship?
In terms of the boy that you dated before, it sounds like you know for yourself that you don't want to actually have sex or a relationship with him. It is very common for our imaginations to fantasise about things we wouldn't actually want to do in real life as a way of exploring things using people/situations we are familiar with in order to do that. For this reason, you shouldn't feel any guilt about fantasises about other people, as they are your own, and you don't have any requirement to be monogamous in your fantasies, as they are actually separate to the people in real life. In fact, when we imagine what someone would be like as a partner, that usually says a lot more about us than about them in real life, crushes and imagined relationships don't actually predict what someone would be like as a partner irl, as our imaginations are filling in how they would act. It is only through dating someone that we can know what kind of partner they are, and we don't always get to date our crushes (which can be hard to accept, but very important to respect). On this, you may find these articles useful/interesting:
Please feel free to share with us what you feel applies/doesn't apply about these articles, and ask any questions you may have!