Guys - How do you know you are the "safe guy"?

If you aren't sure what a "safe guy" is then its basically the guy a girl can have on the back burner who is unattractive (at least to her) and no other girl would want. She doesn't have to worry about you finding someone else because no one else would want you. You are just there as a back up plan if things don't work with a guy (or guys) she is currently talking to. You are loyal and that is your downfall. Also, you may be going on dates with her but she is just wanting some free meals and free movies out of it and she doesn't really want anything else.

Guys - what are signs of this?

Girls - why would you string someone along like this? (I'm not saying that YOU have done this (or are currently doing this) but I would bet you at least know or have one female friend that has done this (or is currently doing this)).
Guys - How do you know you are the "safe guy"?
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