Can anybody help me in my grammar...

I already hired from other company and they're willing to give my asking salary, but i'm not 100% sure if I want to go.
So I'm writing to my boss, something like a negotiation because i was offered by other company a tempting amount but if he will level it to my salary i will not submit my resignation. I've been their employee for 4 years now and I'm handling their top brand (we are in garments, and i worked as a designer), so here's the letter I composed...pls help me fix my grammar or better revise the whole letter....thank you:

dear sir:
I'm writing to you thru e-mail for I can't express my thoughts straightly if we talk face to face. Another company is offering me a new job and a generous salary. I've been thinking this over this past 3 weeks and it really giving me headaches on whether I will submit my resignation or not. But to my surprise just before i decide to give you my resignation letter a co-employee of mine and a close friend submitted her resignation. I'm halfhearted on accepting this offer but the salary that they offered is so tempting. I feel so shame and this isn't my character but I have to do this negotiation. With due respect, I would like you to level my current salary to their offer salary which is 30k/month, based on my accomplishments plus a new brand which I will be handling I think that increase in my salary is possible. If I don't hear from you this week, I will assume that you've waived off this letter.
thank you for understanding.