Dear user, assure
Salaam means giving assurance of harmlessness and protection to the opposite side in the sense that whoever says salaam wants to tell the other person that I want your well-being and safety and that you should rest assured that you are safe from my side as I will not harm you. I wish you well and that I have no evil, wrong and hostile intention towards you. Also, salaam is one of the names of Allah, and it is a form of greeting exchanged between two Muslims.
There are many hadiths (sayings) concerning salaam from the Infallible Imams (a.s.) of which we suffice to mentioning only one:
Imam Sadiq, (a.s.) says: "One of the signs of humility in a Muslim is that he salutes aloud everyone he meets."
In order to get to an appropriate answer, it is necessary to make mention of the following points:
1. Attending Friday Prayers is a religious and political act. It is an act of worship which is highly recommended and desirable; so it is befitting for you to keep up attending it.
2. Based on the narrations passed on to us from the Infallibles (a.s.), we are duty-bound to regard the best meaning of the actions of our brethren in faith for their positive aspects and that we should have positive and benevolent intentions towards them.
The Commander of Faithful, Ali (a.s.) said: He who puts himself in situations of accusation should not blame those who doubt him. He who conceals his secrets will possess the options. Every secret that exceeds more than two persons will spread. Regard the best meaning of your brother's saying and never search for an ill meaning in his saying if there is a probability of good intention.
For further information about the effects and treatment of pessimism vide answer No. 5311 (site: 5484).
Therefore, there are different probabilities as to why the prayer leader of your mosque did not return your greeting. There is a likelihood that he might not have heard your greeting or he might have returned it but you are likely to have not heard it. It is also likely that he may have been mentally occupied and that something might have engaged his mind on account of which he has not heard you or taken notice of you or he might have thought that someone else would return the greeting, and so on.
3. If possible, before prejudging or becoming suspicious, try to talk to him politely and tell him that you greeted him many times but you did not hear any answers from him.