My lover
Today, I finally understand the pain of your lover being other's girlfriend. Sometimes I feel the life is tricky, when you love someone, but she doesn't do the same. Oh, that is life and should be learnt!
I hope this correction helps. In your text you just need to change change:
"being another's girlfriend"
"but she doesn't feel the same"
And here's some other suggestions:
Today I finally understand the pain of your lover having another boyfriend. Life can be tricky when you love someone and she doesn't love you back. Oh, that's life and a lesson to be learnt!
Today I finally understand the pain of loving someone who already has a boyfriend.
Today I finally understand the pain of unreciprocated love. Life can be tricky when you love someone and they don't feel the same. But that's life. (Un-re-sip-ro-ca-ted)
My Lover
Today, I finally understand* the pain of your lover being another's girlfriend. Sometimes I feel that the life is *tricky; when you love someone, but she doesn't *do the same. Oh, that is life and should* be learnt!
*I have finally understood
*deceptive, deceitful
*reciprocate, respond (likewise), respond in the same way
*we have to learn !