Many, under the euphoria of the relationship, seem to go blind and do not notice the signs that the guy wants to leave. Usually these people are very dramatized when their tale comes to an end, and painfully experience the breakup. Be prepared to see the red flag before it hurts.
Steps

Step 1. Consider whether he is thwarting plans or avoiding you
Maybe he stopped constantly calling or texting you during the day (if he usually wrote). This could all be a signal.

Step 2. Listen to conversations
Is he still as interested in talking to you as before?

Step 3. Pay attention to the physical manifestations of feelings
If he wants to leave, he will probably stop hugging or kissing you as often as he used to.

Step 4. Look closely at his behavior with other girls
Does he flirt with them in front of your eyes?

Step 5. Talk to his friends
He may have already told others that he intends to break up with you. At the very least, you will be able to understand if he is happy with the relationship.

Step 6. Does he deliberately communicate with girls whom you dislike?
Did he spend more time with his girlfriends? Perhaps he is hinting at something.

Step 7. If during telephone conversations he constantly says that he is busy, perhaps these are just excuses

Step 8. Does he tell you that he wants to leave?
If so, most likely he wants to date other girls and makes you happy. Maybe he wants to be friends with you who have sex sometimes, or he just wants to leave but lacks the courage.

Step 9. Don't annoy him, behave naturally
Do not think too much and do not create provocative situations.
Advice
- Don't show him your concern.
- If it recedes, do not try to impose.
- If he starts showing these signs, start moving away too. Perhaps he needs time to relax, or he will understand how much you mean to him.
- Don't put it all in your face. Be calm and relaxed.
- Behave naturally.
- Don't be dramatic if this happens. Just say you love him and you will miss him. Say that you will always be there to help him as a friend.
- If a breakup is inevitable, back off and let him do what he wants. Don't make the situation awkward, and then you can remain friends. You may even get back together in the future (but don't count on it too much).
- If all the signals are on your face, pretend you don't care.
Warnings
- Don't worry too much. Which have not be avoided. There is nothing you can do about it, just be yourself. If he does not love you, the way you are - this is his problem, not yours.
- Don't call him several times a day asking what he is doing.
- Don't be the first to part with him. Suddenly, after some time, you find out that he was not going to part with you. However, be prepared and develop the right strategy.
- If he's acting like a bastard, don't whine. Show him that you have self-respect and that he is behaving badly. He should respect you too.
- Don't look back, move forward and learn to face your fears.
- Don't be discouraged, you will soon find the right person.
- Don't humiliate yourself and beg him to stay.
- Don't spend days crying, life goes on. Remember, one day you will meet an amazing man, and this person does not even bother to remember.