Hi, I'd like to help you with your question.
It sounds like your boyfriend has something going on for sure. And it is something he either does not want you to know because it is bad for your relationship, harmful to him or embarrassing.
After four months, you certainly have the right to know what is going on with your boyfriend. This is more than just a few dates, you are both involved with each other and I gather that you are not dating others. So knowing his whereabouts and understanding some of the problem is your right in this relationship.
Contact him on Saturday and ask what has been going on. Be up front with him and tell him that you need to have some idea of what is going on so you do not assume the worst. If he does not give you a straight answer, then you have good reason to be concerned. If he is hiding something from you now, then what will he be like in the future?
Before you contact him, consider your options. Plan what you will say to each response he may have to your question. That way, you are not caught off guard. Plan for the worst case scenario and the best case. It will help you feel more in control of yourself and the situation.
I hope this has helped you,