Enjoying someone's company v. liking them "enough"

Two of my dear friends have been dealing with similar interesting and unfortunate situations recently. It's a situation both I and my ex went through a version of, and some might say we paid for not paying enough attention to it. 

So you have this friend, or this acquaintance, and you're trying to figure out whether your feelings for them go beyond friend/acquaintance-ship. Maybe you've learned that they have feelings for you. Maybe you just like spending time with them so much that you're conflicted about what you're feeling. Whatever. The point is, how do you know where to draw the line between liking someone as a person and liking them enough to be in a relationship with them? What are the ethics of entering a relationship for exploratory purposes? Should you have to feel some romantic-comedy-esque "spark" or intense desire before embarking on the whole relationship thing, or is it cool if you just like to kick it with X or Y person and want to make your kicking it an official thing?

I guess what I'm really driving at here is this: 

What exactly makes a lover different from a friend?

Apart from sexytime fun, of course. Because as hard as I try and try to think about what separates them, I'm coming up empty. I feel like both of the relationships I've been in were like, suddenly I had a new best friend I also got to regularly hook up with and be cutesy and publicly physical with. And even though the ends of these relationships had me feeling like a hot ass mess for days, the level of emotional commitment I felt to them can't even touch the foundations of the emotions I have for some of my friends. But saying that sex is the only difference seems...just somehow fundamentally like I'm doing something wrong, though Idk if it's my friendships or my romances. I have never found that I necessarily like the person I'm dating MORE than I like my closest friends, and honestly I'm not sure I would trust such feelings if I ever developed them. I even get conflicted about choosing to hang out with a partner over hanging out with my besties. 

But I'm getting off-topic. I begin with the above question in order to better understand the point and goal of relationships. I was at an event on Black Love on Tuesday night, and one of the icebreaker questions asked at the event was something to the effect of, what do you look for in a relationship, and my answers were basically the same things I look for in a close friendship. Which leads me to re-realize (because I've addressed this before) that I'm unsure what prompts me to turn friend/acquaintance-ships into relationships besides knowing that the other party is romantically (sexually?) interested in me and me not being actively disinterested in him (or, theoretically, her). And this question has never been posed to me directly, but I'm afraid that if someone asked me, say, what I wanted to "get" out of a relationship, I wouldn't know what to say but sex and companionship...and neither of those things really necessitates the title. I'm fully comfortable giving and receiving the title expecting only those two things though, and it seems a little bit ridiculous to me to expect anything more than those two things going into a title-based situation. 

Where does the l-word come in? (Love.) I...don't even know what that word is supposed to mean with regards to any sort of relationship, but particularly not with a romantic relationship. Do I NEED to get to that level for a relationship to be "worth it"? Can I still just use it to mean something in me resonates with something in you and I like the frequency we're vibing at? If I like the way that spending time with you makes me feel, should I just say that instead of trying to fit it into ambiguous constructs like "love"? Is that revolutionary or am I copping out? Maybe I should be trying to expand the definition of love to be applicable to all those various situations, but...even though I guess that's what I do now, I'm not entirely comfortable with that. Maybe it's a word that should retain some sort of special value, so that everyone knows what you're talking about when you use it.

How do we have legitimate and meaningful interactions when we're not even sure what we mean by the words we're using?

I'm getting off topic again, it seems. It seems to confuse some of my dear friends that I have no problem with what might be called "casual" relationships. By this I mean I can go into a relationship that I know isn't going to last and still be committed to and emotionally invested in that relationship. (This most likely stems from the fact that I conceptualize relationships as transient and ephemeral in nature, thus if I was unwilling to involve myself in romances that I didn't think would last, I would be committing myself to spinsterdom.) And yeah I guess that sounds like I'm just setting myself up to get hurt a lot, but again...that's just part of the way I fundamentally understand the game. I also get a lot of joy and contentment and comfort and satisfaction. 

All this to say, I'm unsure whether I really have even a fuzzily defined line between liking someone as a person and liking them enough to enter into a relationship with them if they expressed interest in something of this nature. I have trouble even imagining what sorts of characteristics would bring someone from one side of this hypothetical line to the other. This means I have nothing on which to even base an understanding of where people are coming from when they're averse to trying relationships with persons whose company (and maybe even affections) they enjoy. I want to understand, though...I really do. Because sometimes my perspective doesn't seem healthy to me.