After possible exposure you can only know whether you are infected by taking a test.
When someone is infected the body tries to fight it off by making antibodies. These antibodies show up with a blood test. People who have these antibodies are called “HIV positive”. This means they are infected.
A test is only really reliable if it’s done 3 to 6 months after possible exposure to HIV. It takes awhile for the immune system to manufactures antibodies. If you test too early these antibodies might not yet be present.
Test results are normally in after two weeks. A “positive” result on a test is always confirmed with a second test.
In the Netherlands most big hospitals have an outpatient clinic where you can be tested.