done said:
why cant I be that amazing person for them?
I don't often answer threads in the Issues section, because I often don't have the answers, though I wish I did. I wish the had the answers for you and everyone else, but I don't.
The only thing I can think of to say is that life is filled with ups and downs. Emotions are like a river, constantly flowing and shifting. When you believe that the present will stretch into eternity, it tends to make everything seem bleak. In reality, you cannot predict your future with any certainty. Tomorrow, you might step out into traffic and get killed by a truck. Tomorrow, you may win the lottery and never have to work again.
Second, you aren't responsible for the actions of others. If you've been attentive, loving and present in your relationships I can see no valid reason that you should be cheated on. In fact, even if you weren't these things, it wouldn't give your ex girlfriends the license to go and cheat on you. It would only give them the license to end the relationship.
Third, make sure you are assertive, rather than letting people walk all over you. If you let people walk all over you, then you'll end up getting used and disregarded.
I hope some of this helps you. If you continue to feel sad for a long length of time, (weeks, or months) you might want to check out getting put on an anti-depressant for a while and/or entering into counseling.