I will use fighting as an analogy in my post.
OP wants to learn VIOLENCE(relationships). So, the general advice is to seek violence in a controlled environment first (aka a boxing gym). We could say" just go to the hood,challenge(=cold approach)a mofo (=woman) et voila . You might get your experience within seconds. But ,obviously OP has his reasons to be scared of this, so we go back to looking at a rather " controlled environment ". Even though we already know that a gym simply doesn't provide REAL ,limitless violence .there are strict rules.
You go to the gym and you'll learn how to spar (= feck a woman). Now mind you, even the hardest sparring session won't ever resemble a real match in the ring (= a ONS ,or FWB ) let alone a streetfight (=a REAL relationship with a strang woman) . Even though you might step inside a gym and face a young,unknown Mike Tyson who'll school you , but the chance this happens is small. (= a nice prostitute who does her work with passion and actually likes you) .
At the end of it all, a trained fighter might have more chances in a streetfight. But anyone with experiences in the Djojo, the ring, and the street will know these are vastly different from each other (= a prostitute, a ONS FWB vs a real long term relationship and eventually living together and/or marriage. )
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I hope my fighting/violence analogy makes sense.
So , a man without xp with women and sex can visit a professional . Even tell and pay her to "make it look like a real fight" =the gf experience. You'll at least have more affinity with women and sex. But, as mentioned before, it teaches you nothing about the nitty gritty of relationship dynamics. To refer to my first piece of writing, it might even give you a false sense of reality. In real life you wont hear " olala so handsome papi, me want fecki sucki long time you ".
The ONLY way is to actually put yourself in the (for you) most vulnerable positions; and that's facing rejection aka cold approach.
Its weekend. The cities are filled with women wanting a good time. A dope wingman ,some social skills and confidence and anything might happen. But you'll have to be there where the fun's at. And not be a socially awkward person qho hides in the corner waiting until "she " walks up to you. That's a luxury only (cute and pretty) women have. Men will have to take risk left and right to make shyte happen. And that goes for any area of life.
You can visit a 100 prostitutes, when you are in a relationship the rules change dramatically. Even better; a prostitute at least has rules (you pay ,she'll do xyz). A "normal" woman doesn't owe you shyte. A prostitute must "fight" with strict rules and regulations. A "normal " woman (aka the streetfight) can bite, stab or shoot you. Anything goes and all is fair in love and war is the saying right?