帮我检查有没有语法错误?顺便帮我润色一下吧.

已经写得相当不错了,仅有的几处语法或修辞疏漏我帮你试着改写如下：

We have been good friends (since=>for) 10 years (ago, =>and) we know each other well. I know (she=>that she's) had a bad marriage and lost (connects=>contact) with (his=>her) son. So, she has been living alone for a long time. (With the increase of age=>As she grows older), she feels (more lonely=>lonelier) than ever.
Niu ’mother (was=>删除) passed away In July 2012, I (saw=>met) Mr Xiao (for the first time) at (+the) funeral. Niu told me that she has confirmed (the=>her) relationship with Mr Xiao. (On=>During) Spring Festival in 2013, Mr. Xiao returned to Shanghai and they (get=>got) married. Since then, I (+got to) know more about them. (And=>删除） I (also know=>found out that) Mr. Xiao (was=>had been) living a single life for a long time too, they (have the=>both had) similar experience on marriage and (both of them=>therefore) want to have a partner (to=>so they can) take care of each other. (In=>At) her birthday party(+,) I (+could) feel that their love is (true,=>genuine.) (according to their=>With such a) solid colleagues friendship,I believe they will be happy in their (later=>future) years (+together).