How can I tell if my boyfriend is cheating on me?

How can I tell if my boyfriend is cheating on me without asking him straight out because I know he would never admit it unless I had some hard evidence in my hands?

We had been together for 4 months when I found out that when we were first starting to date that he was still sleeping with other girls but I didn't confront him but now I am not sure if he is still doing it or not or when it stopped?

Why do guys cheat on girls if they tell her they love her and get everything that they want from her?

What should I do?

How can I tell if my boyfriend is cheating on me?
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