The game is great, but it is designed to be more of a thriller with a love-story weaved into it, where you can pick the person you want the MC to fall in love with. Sleeping around is possible in the story, but usually not without consequences.
What I usually do with these type of VN's is play through it normally once, choosing the love interest I find most appealing (in this case, for me that was Vanessa), and then do several other playthroughs where I quickly Fast Forward/Skip (keep CTRL pressed) through all the parts that are basically the same anyways. You can do multiple playthroughs quite quickly that way.