The menstrual cycle periodicity is dependent up on the hormonal
cycle in the body. Usually in normal cycle, the period appears 14 days after the egg release. Thus it is not at all dependent upon the change in partner. It is likely that you could have unprotected sex during your fertile window and you might have become pregnant.
Even otherwise, 4 days before or after variation in menses is considered as normal.
Do you have any stress? Stress does cause irregularity in menses.
If you do not get menses even after one week more, you may perform urine pregnancy
test and/or ultrasonography
for detection of pregnancy. These tests done earlier may not be conclusive and reliable. Beta hCG
test is conclusive even 2-3 days after the missed period.
I am sure your misbelief has been taken care of.