Having sex with others until you're 'exclusive'?

Is it just me who finds it hard to get my head around the fact it should be accectable and normal/modern dating behaviour that you can have sex with multiple people, whilst 'dating' ( messaging, expressing an interest, going on dates, seeing if a relationship is on the cards) someone? I feel 'cheated' on and I can't accept that this person is interested/likes me if they can easily do that whilst expressing an interest in me. It's like this is now 'how it is' in modern dating and I find it horrifying... Am I the only one?
Having sex with others until you're 'exclusive'?
Post Opinion