An apology letter to boyfriend needs to be written with love, kindness and honesty. Accept for the mistake you have done, this letter cannot be formal, such letter needs to be written from heart. There are various ways to apologies to your boyfriend you can call him for dinner, or movie or write a poem. If there is situation where your boyfriend is not ready to hear you, then you can take help of the letter and explain what you want.
2nd June, 2012
Name/Title Mary Roe
Address 795 E Dragram
City, State, Zip Code Tucson, AZ, 85705
I am sorry for not attending your birthday party. I know you where expecting me to come but at last minute, dad got a stroke and we had to take him to hospital. I was completely tensed during that time and did not realize to call and inform you.
I have checked your missed calls on my cell but had no time to call you back has situation was out of my control. I had to take care of him and do all the formality that doctor asked for.
I hope you understand my situation. I will be waiting for your call.
With lots of love