Going to therapy makes me feel like I'm never going to be in a relationship.
Shouldn't therapy have the opposite affect from that?
Going to therapy has made me realize that I just can't see myself being happy in a relationship.
If not being in a relationship is going to make you a happier person then more power to you. Not everyone needs to be in a relationship to feel complete. You should be open to the idea of being in one but you don't need tone to be happy, that's for sure.
I think I'm addicted to causual sex.
If you think you're a sex addict, more therapy should help you work out these issues.  This will make it easier to find a fulfilling relationship!