I did the test 29 Nov. And I did again a test today, the one that is showing the weeks (CLEARBLUE) and came 3+ .
You said "I had sex once with him on 15th Nov. ... I did a test in the morning and came positive." You don't mean on the morning after you had sex with him (i.e., November 16), do you? If so, don't worry, tests don't measure pregnancy that fast! If you took a test November 16 and got a positive, it is certainly from earlier than November 15.
If on the other hand, "I did a test in the morning and it came positive," means you did a test *this* morning, (i.e., November 29), it could be either guy. But the timing points to your London friend due to you having been having sex around the time you presumably ovulated, and you two gave it lots of chances.
That said, I think that unless your menstrual cycles are super long, like five weeks from first day of bleeding to first day of bleeding, the fact that your period came on October 23, and your beloved from London was with you having lots of sex from the 7th to the 9th of November, is almost definitive. In other words, Sir Lancelot from Britain is in a much more convincing position to be the daddy than Signore Nice Guy, even if Signore had an errant flying sperm when he pulled out.
Get an ultrasound in week 7 (counted from the first day of your last period, not from when you guess conception was), and ask them to confirm your date from the crown-to-rump measurement of the embryo. Remember that the medical way to count pregnancy is from the first day of your last period, for example, today November 30 you are officially 5 weeks 3 days (and that would be how it is counted no matter which guy is the dad). So see the doctor in a couple of weeks, and things should be a little clearer.