Don't do a 2-3 hour session with the same sp, see 3 different sps instead.
If you're only looking for a sp to take care of your sexual needs then you're still gonna go back to sex with yourself afterwards.
Like you said yourself and read my previous post, if your problem with girls is because you're introverted, than seeing different sps for 1hy each will allow you to practice more interacting with girls. Social skills are what you need. Learn to chat them up, to flirt....And you don't have to see independents, reputable agency girls are fine, too. Just don't blow all your money on the same girl. See a bunch of them.
Your goal to seeing sps shouldn't be for an instant gratification and a temporary substitute for a gf. Your goal should be to learn and to practice the necessary social skills with sps so that it'll help you get laid for free in the future.
Better yet, ask them to role play, pretend you guys meet in the dorm hallways, library, classroom, cafeteria, etc.....And chat them up, flirt with them, ask them to have a soda with you, go back to your room, etc.....They're gonna say yes. Or ask them to shoot you down at first and you practice being persistent and thick skined. You'll get more used to do this and build some confidence, and hopefully can transfer the skills on girls in real life.
Again, this is very important, if you don't learn and only look for a sp to take care of your sexual needs then you're still gonna lead a life of wanking yourself.
You're only 20! You shouldn't be looking for the same things in this hobby as older Merbites! We're too fucking old to get 20 yr old girls to fuck us for free. God I wish I was 20 again.