Hi Spiderman23,
Whilst a lot of different factors can cause delayed or absent periods, sex isn't generally one of them. It's not unusual for high arousal, orgasm and the uterine contractions that come with them to mean you see the flow a little earlier than you might normally expect.
That doesn't mean you can't still have and enjoy all kinds of sex together though! You can e.g. put a towel down and go ahead as you would at any other time of the month. Alternatively, using things like tampons, diaphragms and menstrual cups can limit the appearance of blood and allow you to enjoy physical intimacy with your boyfriend and explore things you both enjoy without the mess (although tampon + vaginal intercourse = bad idea). This article has more on having sex on your period:
Sex, period.
For more on periods and sex, check out
What do you want to know about periods and sex?