In my case, it made things significantly worse in the long run. Granted, it's a unique case and partially my fault. It was my freshman year of college, and I essentially became obsessed with this girl shortly after I arrived here, partially due to not knowing anyone else (I had talked with her online beforehand, so she was one of the first people I actually met in person). Sad to say, I spent almost that entire year either alone (including hours a day talking to her online) or with her. We were "friends" for a couple months before she finally brought up the possibility of a relationship (since I was too chickensh!t, naturally) - but she seemed unsure of what she wanted at that point, which should've been a big red flag, but due to my obsession I walked right into it anyhow. She could smell my desperation and used it to her advantage, teasing me with signs of interest in other guys and actually breaking up with me twice before I decided to sever all ties. This all went on over a period of several months.
In the end, the "relationship" (and I use that term loosely, given the lack of... er, intimacy that occurred) had two lasting effects on me. The first is that I'm now even more convinced than ever that I should just completely avoid dating and girls; before her, all my worries had focused on flat-out rejection, but she made me realize that even someone who agrees to enter into a relationship with me might not actually be romantically attracted to me (I'm not sure whether she was just using me, was too nice to reject me since we were already good friends and she was a bit of a loner too, or both). In other words, going through a period where I believed - shocking as it was - that a girl could actually be attracted to me, only to ultimately learn she probably never was, left me permanently scarred and extremely cynical (girls who are "too nice" to reject a guy they're unsure or lukewarm about, take note! You're not doing them any favors!). The second effect was to rob me of that crucial freshman year in which, despite my rather severe SA, I probably would've at least met a few friends had I not been so consumed by my dead-end obsession with this girl. Of course, the following year I had to start fresh, and by that point groups and cliques were already established and I'd sort of missed the boat.
Again, a lot of what happened in my case was partially or fully my own fault. But a couple of things to take away from it, I guess: 1) make absolutely sure to maintain existing friendships and/or strive to form new ones even after you get into a relationship - if you don't think you can make yourself do this, don't get into the relationship - it's absolutely not worth it no matter how tempting it may be, cause 95% of relationships aren't going to last more than a few months! And 2) be wary of allowing your self-esteem and self-worth to become too attached to the other person's approval. By going from being a guy with a terrible self-image WRT girls to thinking I was actually attractive to a fairly good-looking girl, only to have it all ripped out from under me later on, I did such damage to my self-esteem that I honestly don't think I'll ever be able to trust a girl again, even if she shows signs of interest (it's been 3 years now and I still feel that way).