First, think about why it is in your head crept unpleasant thoughts. Why are you suddenly began to suspect his beloved of infidelity? Perhaps you are just not happy with themselves and are afraid that he will find another, more attractive girl. The cure for this one – take care of your appearance, become confident, and all suspicion will dissipate, because you will know what better you he can't find anyone.
If the problem lies in it, you really need to check how he is loyal to you. Watch out for his behavior. The first sign that the guy brought another girl – a lack of time. If you've held him every minute, and the last time you see it less likely he has someone else.
He can say what very tired, I started going to the gym, he had a hobby, he is missing his friends, etc. Just once check it. Accidentally find yourself there, where, according to him, it needs to be and look he lied to you or not. If he lied, it was for a reason.
Find out passwords from social networks. Just to know he shouldn't. Go to its page, read the message. Quite often the whole truth about cheating POPs up that way. Also help you can reach his cell phone. View incoming and outgoing calls, correspondence.
Communicate more with his friends. Some of them may inadvertently give your partner if he has another. Directly they will not tell you this, but can pierce, if you ask about where they are, for example, walking out last week. If your young man said he was with them, and they don't know it, you have to have a serious talk with a loved one.
Arrange a Frank discussion. Ask him not to lie to you, if he even slightly cares about your relationship. Ask him directly who he's seeing. Explain to him that you are not married, lie makes no sense. If he liked another, better out with it than cheating and hurting you. Look him in the eye when he answers your questions. If you know your boyfriend, you'll know he's lying to you or telling the truth.
Do not jump on the favorite accusations if you have no evidence. So you're only hurting your relationship by showing him that you don't trust. Be vigilant, but don't get excited just because you saw something.