Can Sperm Survive Three Months?

Hi. I am 18 weeks and 5 days pregnant. My due date is July 21. My last menstrual period was October 15 therefore I conceived around October 29. I have had two ultrasounds, both confirming the due date, one at 14 weeks and one at 18 weeks and 2 days. I have been with my boyfriend for three years. On July 22 I was with someone other than my boyfriend, only one time. At the time I had forgotten my pills three days in a row so we used withdrawal and then two days later I took the Morning After Pill, just in case. I started my period about four weeks later. It was quite heavy and I also had some breakthrough bleeding later on that month after that period had ended. I haven’t been with him since, and on September 9, I quit taking the pill altogether. I had a normal menstrual cycle on October 15, it was pretty heavy also and lasted about five days. I conceived around October 29th and have had no bleeding what-so-ever since my last period. The difference between when I conceived and when I was with the other man was about three months and seven days. I’m pretty sure that sperm only live days and not weeks, certainly not months, and that it would not be possible for sperm from intercourse from three months ago to still be around at the time of conception. I know it is somewhat far-fetched, but I have been having nightmares and racing thoughts thinking of what if that were the out come, it would be devastating for many people. I don’t have anyone else to confide in and I wanted to ask an expert rather that just anyone.
Can you please answer my question if it is possible that the man I was with on July 22 could be the father of my child conceived on or around October 29. Thank you very much.

Niki