Hey there, Hel. I want to add something else in here for you.
Protecting our hearts is something that is as much a thing we need to do as other people do. In other words, at least half the job of protecting our hearts in an interaction or relationship is on us, not the other person. It sounds to me like you may not be doing much of that.
It's most typical for relationships in your age group to only last a few weeks or months. I know that can really suck (I remember), but it's also just a reality. It's also not usually because people are being jerks so much as because at this stage of development, people are in a state of pretty constant change, so who they feel like and what they want can change, which tends to have an impact on dating, friendships and other relationships. Often even when they do last longer then, it's about things like trauma bonding (that was the case with my most mutually emotionally intense relationships in my teens, for sure) or people feeling like it's not okay for them to move on, even when they want to, because so often teens are or feel held to standards about relationships that are for much older people in a different time of life.
So, knowing something like that, just as an example, some things that yo can do to protect your heart are things like making sure your expectations are realistic: for instance, it's wholly likely this one may not last for years, if that, too, even if this guy is great, you're great, and everyone cares about each other. Knowing that, you can also know not to go 300% in emotionally, but instead, move more slowly and gradually. Does that make sense?
I think something else to keep in mind when it comes to expectations is to understand and accept where you're all at developmentally, The behaviour you described in that last paragraph about the video game then the group chat all sounds really normative for me for a lot of people your age. You say you want to know he's serious, but not only are you guys young, you've also only been dating for a month. We can just only truly feel so much for someone we are just getting to know, and in a new dating relationship. Love isn't something we can usually develop that fast at any age -- extreme like, sure. Infatuation? Oh boy, yes. Sexual and romantic desires? Yep.
My point in saying all that is that we're bound to be disappointed or gets our hearts busted if our expectations of people, and what we want from them, isn't realistic or sound.
I wouldn't ask someone I had been dating for a month if they see our relationship as serious, because a relationship that's only a month old really can't -- and IMHO, for healthy boundaries, shouldn't -- be that serious. We need time to figure out how we feel about people, time to grow and nurture a relationship to sort out what we want from it and what it is for us, and time and space to feel and learn to understand our own feelings.
Instead, I'd suggest you sit with yourself and your fears and feelings, and see if you can't sort out what you would want from a statement like that: what are you looking for? What do you need from that, and is it -- as it may well be -- something you can actually give to yourself, like not getting too invested in new relationships right at the gate? Like not doing things, like kinds of physical intimacy, or commitments, before trust is built with someone for you to have the kind of safety you want? Get what I mean?
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead