He was my first but he just played with me and said he still misses his ex. Why guys use girls like this?

[Deimy]

[quaranta]

It's not "guys", it's this guy. And girls can do really the same...
It happens most often when you get a partner who is not seeing you like an actual partner but like a rebound. Stay away from potential partners who broke up with their exes too recently, they have to elaborate and grow past their break up to really get over them. Rebound relationships never work, in general... Because they are not genuine, they driven by their fears and their need to replace their ex, but without any time to work over the breakup and interiorize what happened, to be ready for a real relationship later, with a really selected partner, not the first one who comes across. (I actually think girls do this even more than guys but that's my perception).
On the other side: don't give too much or open too much if your partner (or guy you are getting to know) is not vulnerable the same to you. Keep it balanced. Of course you can't do anything against actual "lies", you can't predict them sometimes, but you can surely sense when the partner is not as committed as you are and that's when you have to stop yourself until he gets to your same pace...
Now, don't be back with this guy. If you move on and he crawls back, do not accept him, otherwise you'll reward what he did and he will learn that he can actually pull and push you anywhere in his life and that is "ok". Don't set this rule, so don't be back when he will possibly crawl back.

[Anonymous]

Nothing kills the joy of a relationship like that nagging feeling that your boo still isn't totally over his or her ex.

If your new boyfriend is constantly talking about his ex, spending time on the phone with her, meeting up with her without including you, comparing you in a way that makes you feel less than her, these all point to the possibility of him still being connected to her in some way

But honestly, any behavior that's giving you a gross feeling in the pit of your stomach is enough to consider re-evaluating your relationship status. Something is a red flag if it's causing you significant and ongoing upsetting feelings like hurt, worry, suspicion, anger, insecurity, frustration, or feeling disrespected.

Good luck.

[slatyb]

Because they are young and haven't figured out how to behave.