Welcome back binayak. Don't worry, your condition doesn't look like any sexually transmitted infection.
It is cutaneous allergic reaction to brufen called as "fixed drug eruption". glans penis is one of the common area. Don't stress much, it will heal by itself after few days. If u are in doubt, visit a dermatologist, ur doctor may perform drug challenge by giving the same drug again and u may noticed another blister on the same area. One more thing, always have protected sex, good for both the partners...