Hey there, dark_sunshine. I'm happy to pitch in here.
So, I'm a queer person -- for me that means that I am and, since I was a kid, have always been, attracted to people of all genders -- and same-sex marriage wasn't an option for me growing up (I'm turning 50 this spring). But I also have long been politically opposed to marriage as an institution, so on the whole, I was pretty much always clear that whatever the gender of my partners, I did not want to get married to anyone, ever. For those reasons and some others (waiting for marriage just wasn't a thing for me culturally, period), the idea that I was choosing to be sexual with others before marriage or not simply wasn't part of my sexual decision-making process. And because I'm still politically opposed to marriage as an institution, it's probably obvious that this whole framework of if I have regrets about waiting for marriage or not just doesn't apply to me.
I started being sexual with people by choice in my early teens: a little early compared to many of my peers then, a lot earlier than most people now. I have had many partners: again, in my generation, more than many people, and for people of your generation, probably considerably more than nearly anyone will likely have in a lifetime unless your generation's sexual behaviours change a lot over the next few decades (which they might, who knows). In my case, that's close to about 100 people, to be transparent about it. That's on the high side for many people my age, but it's not super abnormal, especially for people who were in the kind of scenes I have been and people who have done sex work. But I don't often share that openly with people your age, because I've found a lot of folks in your generation get really freaked out about the numbers of partners of people from mine, and use words like "promiscuous" which isn't actually even the right word (having many partners does not necessarily equal not being selective, which is what that word means). That's not too surprising, of course, since a lot of you have grown up either with or after a great deal of abstinence-only/evangelical attitudes and messaging about sex that teach things like that it's better to wait until marriage (even though it hasn't ben very common to do that for most of history, with the exception of way back when when people were getting married in their early teens, usually before some of them had any interest in sex at all, including within marriage), a lot of sexual shaming, and with simply different sexual culture than mine.
I do think it's worth noting that 3 partners is not a lot of partners by anyone's realistic standards including right now: realistically, most people even your age will have 4-7 partners over a lifetime on average, based on both studies and anecdotes.
Just about everyone I have ever had as a sexual partner, unless it's been a one-night-stand where we didn't talk much about our histories (and even in those, I usually have), knows the basics of my sexual history. One of my parents has a pretty good sense of my history, the other only kind of (I left home at 15 and didn't talk to them again until I was in my mid-twenties). Not knowing all of my history isn't about me hiding anything, it's just about no one asking.
I don't have regrets about the bulk of my sexual choices. I've really enjoyed most of my sexual life, I've really enjoyed most of the people I have been sexual with, and a lot of my sexual interactions have turned into relationships that have lasted over many years that I have valued (almost all of them friendships, but some of them domestic/partnership relationships). It wasn't a game plan, mind -- I'm not actually sure what you mean by that -- rather, it's just been me deciding what I wanted based on the opportunities I have found or sought out, and how I have felt at the time, much like my life has gone when it's come to my friendships, for example.
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